Voice-activated personal alarm

ABSTRACT

A self-locating remote monitoring system ( 750 ) includes a supervising base station ( 754 ) and one or more remote monitoring units ( 752 ). A remote unit ( 752 ) includes a navigational receiver ( 756 ) operating with an existing navigational system for providing a remote unit location ( 759 ) and includes a transmitter ( 758 ) for communicating the location ( 759 ) to the base station ( 754 ) for display ( 772 ). The remote unit ( 752 ) includes one or more physiological/environmental sensors ( 760 ) for monitoring at the remote location. In a specific embodiment a change in sensor status ( 761 ) results in the status and the location being transmitted to the base station ( 754 ). The base station ( 754 ) includes alarms ( 776 ) and displays ( 772 ) responsive to the change in status. One embodiment defines a man-over-board system ( 300 ) which combines water immersion ( 308 ) and distance ( 334 ) from the base station ( 318 ) to trigger an alarm ( 332 ) and begin location tracking ( 324 ). Another embodiment defines an invisible fence system ( 1020 ) which uses location ( 1035 ) and time ( 1039 ) to define boundaries for containment and exclusion. Another embodiment includes a weather surveillance radar receiver ( 1188 ) providing weather parameters ( 1189 ) within a weather region ( 1193 ) and defines a remote weather alarm system ( 1180 ). The weather alarm system ( 1180 ) uses the weather receiver ( 1188 ) to monitor weather within a defined region ( 1193 ) and to provide the base station ( 1184 ) with location ( 1187 ) and weather parameters ( 1199 ) if the parameters fall outside defined limits ( 1195 ).

CLAIM OF PRIORITY

[0001] This Application claims priorty from a copending InternationalPatent Application, No. PCT/US95/13823, filed Oct. 26, 1995, having anInternational Publication No. WO 96/13819, and International PublicationDate May 9, 1996.

TECHNICAL FIELD

[0002] This invention relates to personal alarm systems and inparticular to such systems transmitting at a higher power level duringemergencies.

BACKGROUND ART

[0003] Personal alarm systems are well known in the art (see for exampleU.S. Pat. Nos. 4,777,478; 5,025,247; 5,115,223; 4,952,928; 4,819,860;4,899,135; 5,047,750; 4,785,291; 5,043,702, and 5,086,391). Thesesystems are used to maintain surveillance of children. They are used tomonitor the safety of employees involved in dangerous work at remotelocations. They are even used to find lost or stolen vehicles andstrayed pets.

[0004] These systems use radio technology to link a remote transmittingunit with a base receiving and monitoring station. The remote unit isusually equipped with one or more hazard sensors and is worn or attachedto the person or thing to be monitored. When a hazard is detected, theremote unit transmits to the receiving base station where an operatorcan take appropriate action in responding to the hazard. The use ofpersonal alarm systems to monitor the activities of children has becomeincreasingly popular. A caretaker attaches a small remote unit, nolarger than a personal pager, to an outer garment of a small child. Ifthe child wanders off or is confronted with a detectable hazard, thecaretaker is immediately notified and can come to the child's aid. In atleast one interesting application, a remote unit includes a receiver andan audible alarm which can be activated by a small hand-heldtransmitter. The alarm is attached to a small child. If the childwanders away in a large crowd, such as in a department store, thecaretaker actives the audible alarm which then emits a sequence of“beeps” useful in locating the child in the same way one finds a car ata parking lot through the use of an auto alarm system.

[0005] A number of novel features have been included in personal alarmsystems. Hirsh et al., U.S. Pat. No. 4,777,478, provide for a panicbutton to be activated by the child, or an alarm to be given if someoneattempts to remove the remote unit from the child's clothing. Banks,U.S. Pat. No. 5,025,247, teaches a base station which latches an alarmcondition so that failure of the remote unit, once having given thealarm, will not cause the alarm to turn off before help is summoned.Moody, U.S. Pat. No. 5,115,223, teaches use of orbiting satellites andtriangulation to limit the area of a search for a remote unit which hasinitiated an alarm. In U.S. Pat. No. 4,952,928 to Carroll et al., and inU.S. Pat. No. 4,819,860 to Hargrove et al., the apparatus provides forthe remote monitoring of the vital signs of persons who are not confinedto fixed locations.

[0006] Ghahariiran, U.S. Pat. No. 4,899,135, teaches a child monitoringdevice using radio or ultra-sonic frequency to give alarm if a childwanders out of range or falls into water. Hawthorne, U.S. Pat. No.4,785,291, teaches a distance monitor for child surveillance in which aunit worn by the child includes a radio transmitter. As the child movesout of range, the received field strength, of a signal transmitted bythe child's unit, falls below a limit and an alarm is given.

[0007] Clinical experience in the emergency rooms of our hospitals hastaught that a limited number of common hazards account for a majority ofthe preventable injuries and deaths among our toddler age children.These hazards include the child's wandering away from a safe orsupervised area, water immersion, fire, smoke inhalation, carbonmonoxide poisoning and electrical shock. Child monitoring devices, suchas those described above, have been effective in reducing the number ofinjuries and deaths related to these common preventable hazards.

[0008] However, considering the importance of our children's safety,there remains room for improvement of these systems. One such area forimprovement relates to increasing the useful life of a battery used topower the remote unit of these toddler telemetry systems, as they havecome to be called.

[0009] The remote unit is typically battery operated and, in the eventof an emergency, continued and reliable transmission for use in statusreporting and direction finding is of paramount importance. In otherwords, once the hazard is detected and the alarm given, it is essentialthat the remote unit continue to transmit so that direction findingdevices can be used to locate the child.

[0010] The remote unit of most child monitoring systems is typicallyquite small and the available space for a battery is therefore quitelimited. Despite recent advances in battery technology, the useful lifeof a battery is typically related to the battery size. For example, thelarger “D” cell lasting considerably longer than the much smaller andlighter “AAA” cell. Though the use of very low power electronic circuitshas made possible the use of smaller batteries, a battery's useful lifeis still very much a factor of its physical size, which, as statedabove, is limited because of the small size of a typical remote unit.Therefore, additional efforts to reduce battery drain are important.

[0011] Given that much reliance is placed on the reliability of anychild monitoring system, it would be desirable for the remote unit totransmit at a low power or not at all when no danger exists. In this waybattery life is increased and system reliability is improved overallsince the hazards are usually the exception rather than the rule.

[0012] Additional U.S. Patents of interest with respect to thiscontinuation-in-part include: 3,646,583; 3,784,842; 3,828,306;4,216,545; 4,598,272; 4,656,463; 4675,656; 5,043,736; 5,223,844; 5,311,197; 5,334,974; 5,378,865.

DISCLOSURE OF INVENTION

[0013] It is an object of the present invention to provide a personalalarm system in which the battery operated remote unit normallytransmits at low power and switches to a higher power when the distancebetween the remote unit and base station exceeds a predetermined limit.

[0014] It is also an object of the present invention to provide such asystem which includes sensors for the hazardous conditions typicallyconfronting young children.

[0015] It is a further object of the present invention to provide such apersonal alarm system which includes a periodic handshake exchangebetween the remote unit and base station to demonstrate that the systemcontinues to be operational.

[0016] In accordance with the above objects and those that will becomeapparent below, a personal alarm system is provided, comprising:

[0017] a remote unit including radio transmitting means and radioreceiving means;

[0018] the remote unit transmitting means being able to transmit at morethan one power level and defining a higher power level;

[0019] a base station including radio transmitting means and radioreceiving means;

[0020] the remote unit and the base station being in radio communicationand defining a separation distance between the remote unit and the basestation;

[0021] measuring means for determining whether the separation distanceexceeds a predetermined limit;

[0022] means responsive to the measuring means for causing the remoteunit transmitting means to transmit at the higher power level when theseparation distance exceeds the limit; and

[0023] alarm means for indicating when the separation distance exceedsthe limit.

[0024] In one embodiment of the invention, the base station transmits aperiodic polling signal and the remote unit monitors the field strengthof the received polling signal. If the received field strength fallsbelow a limit, corresponding to some maximum distance between the twodevices, the remote unit transmits at high power. The signal transmittedat high power includes an indication that transmission is at high power.When this signal is received by the base station, an alarm is given. Theremote unit also is equipped to detect one or more hazards.

[0025] In another embodiment of the invention, there are multiple remoteunits each able to identify itself by including a unit identificationnumber in its transmitted signal. The remote unit is equipped to detectone or more hazards and to identify detected hazards in itstransmission. The base station is able to display the transmitting unitidentification number and the type of any detected hazard.

[0026] In another embodiment, the base station, rather than the remoteunit, measures the field strength of the received remote unittransmission and instructs the remote unit to transmit at high powerwhen the received field strength falls below a preset limit.

[0027] In another embodiment, the remote unit includes both visual andaudible beacons which can be activated by the base station for use inlocating the child.

[0028] In another embodiment, the remote unit includes a panic buttonwhich the child or concerned person can use to summon help.

[0029] In another embodiment, the base station includes the ability toinitiate a phone call via the public telephone system, for example byinitiating a pager message to alert an absent caretaker.

[0030] In another embodiment, the remote unit includes a globalpositioning system (“GPS”) receiver which is activated if a hazard isdetected or if the child wanders too far from the base station. Theremote unit then transmits global positioning coordinates from the GPSreceiver. These coordinates are received by the base station and used inlocating the child. In an alternative embodiment, the remote unit isattached to a child, pet or vehicle and the GPS receiver is activated bycommand from the base station. The global positioning coordinates arethen used by the base station operator to locate the remote unit.

[0031] In another embodiment, the remote unit is worn by an employeedoing dangerous work at a remote location such as an electrical powerlineman repairing a high voltage power line. The remote unit is equippedwith a GPS receiver and an electrical shock hazard sensor and the remoteunit will instantly transmit the workman's location in the event ofelectrical shock. The device will permit an emergency medical crew torapidly find and give aid to the injured workman and possibly save alife.

[0032] It is an advantage of the present invention to periodically testsystem integrity by exchanging an electronic handshake and giving analarm in the event of failure.

[0033] It is also an advantage of the present invention to prolong theremote unit battery life by transmission at low power in the absence ofa defined emergency.

[0034] It is also an advantage of the present invention that the systemis able to detect and give alarm for a number of common and dangeroushazards.

[0035] It is a further advantage of the present invention to permitrapid and precise location of the remote unit which is equipped with aGPS receiver.

BRIEF DESCRIPTION OF DRAWINGS

[0036] For a further understanding of the objects, features andadvantages of the present invention, reference should be had to thefollowing description of the preferred embodiment, taken in conjunctionwith the accompanying drawing, in which like parts are given likereference numerals and wherein:

[0037]FIG. 1 is a block diagram of a personal alarm system in accordancewith one embodiment of the present invention and transmitting atselectable power levels.

[0038]FIG. 2 is a block diagram of another embodiment of the personalalarm system illustrated in FIG. 1 including multiple remote units.

[0039]FIG. 3 is a block diagram illustrating another embodiment of thepersonal alarm system in accordance with the present invention.

[0040]FIG. 4 is a pictorial diagram illustrating a preferred messageformat used by the personal alarm system illustrated in FIG. 2.

[0041]FIG. 5 is a pictorial diagram illustrating another preferredmessage format used by the personal alarm system illustrated in FIG. 2.

[0042]FIG. 6 is a block diagram illustrating an embodiment of thepersonal alarm system of the present invention using the GlobalPositioning System to improve remote unit location finding.

[0043]FIG. 7 is a pictorial diagram illustrating a base station andremote unit of the personal alarm system of FIG. 1, in a typical childmonitoring application.

[0044]FIG. 8 is a pictorial diagram illustrating a remote unit inaccordance with the present invention being worn at the waist.

[0045]FIG. 9 is a pictorial diagram illustrating a mobile base stationin accordance with the present invention for operation from a vehicleelectrical system

[0046]FIG. 10 is a-pictorial diagram illustrating a base station inaccordance with the present invention being operated from ordinaryhousehold power.

[0047]FIG. 11 is a block diagram illustrating a man-over-board alarmsystem in accordance with one aspect of the present invention.

[0048]FIG. 12 is a block diagram illustrating another embodiment of theman-over-board alarm system

[0049]FIG. 13 is a block diagram illustrating an invisible fencemonitoring system according to another aspect of the present invention.

[0050]FIG. 14 is a pictorial diagram illustrating a boundary defining ageographical region for use with the invisible fence system of FIG. 13.

[0051]FIG. 15 is another pictorial diagram illustrating a defined regionhaving a closed boundary.

[0052]FIG. 16 is another pictorial diagram illustrating a defined regionincluding defined subdivisions.

[0053]FIG. 17 is a block diagram illustrating another aspect of theinvisible fence system

[0054]FIG. 18 is a block diagram showing a fixed-location environmentalsensing system according to another aspect of the present invention.

[0055]FIG. 19 is a block diagram of a personal alarm system includingnavigational location in which the geometric dilution of precisioncalculations are done at the base station.

[0056]FIG. 20 is a block diagram showing an invisible fence alarm systemin which the fence is stored and compared at the base station.

[0057]FIG. 21 is a block diagram illustrating a man-over-board alarmsystem

[0058]FIG. 22 is a partial block diagram illustrating a one-way voicechannel on a man-over-board alarm system.

[0059]FIG. 23 is a partial block diagram illustrating a two-way voicechannel on a man-over-board alarm system.

[0060]FIG. 24 is a block diagram illustrating an invisible fence system

[0061]FIG. 25 is a pictorial diagram illustrating geographical regionsfor an invisible fence system

[0062]FIG. 26 is a table defining a curfew for an invisible fence system

[0063]FIG. 27 is a block diagram illustrating another embodiment of aninvisible fence system

[0064]FIG. 28 is a partial block diagram illustrating a base stationconnected to a communication channel via a modem.

[0065]FIG. 29 is a partial block diagram illustrating an alarm systemincluding an oil/chemical sensor, and all sensors activatingtransmission at a higher power level.

[0066]FIG. 30 is a block diagram illustrating another embodiment of apersonal alarm system.

[0067]FIG. 31 is a partial block diagram illustrating specific circuitsused to select a transmission power level.

[0068]FIG. 32 is a partial block diagram illustrating other specificcircuits used to select a transmission power level.

[0069]FIG. 33 is a block diagram illustrating a specific embodiment of apersonal alarm system.

[0070]FIG. 34 is a block diagram illustrating a weather alarm system

[0071]FIG. 35 is a pictorial diagram representing a specific embodimentof a weather region.

[0072]FIG. 36 is a pictorial diagram illustrating another specificembodiment of a weather region.

[0073]FIG. 37 is a partial block diagram illustrating a conditionalactivation of a navigational receiver for a weather alarm system.

[0074]FIG. 38 is a block diagram illustrating another specificembodiment of a weather alarm system.

[0075]FIG. 39 is a block diagram illustrating a specific embodiment of aremote monitoring unit.

[0076]FIG. 40 is a block diagram illustrating another specificembodiment of a remote monitoring unit.

[0077]FIG. 41 is a partial block diagram illustrating a plurality ofsensors in a specific embodiment of a remote monitoring unit.

[0078]FIG. 42 is a partial pictorial diagram illustrating a typicalstatus vector.

[0079]FIG. 43 is a partial block diagram illustrating an input deviceconnected for providing the value of a second variable in a specificembodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0080] With reference to FIG. 1, there is shown a block diagram of apersonal alarm system according to one embodiment of the presentinvention and depicted generally by the numeral 10. The personal alarmsystem 10 includes a remote unit 12 and a base station 14. The remoteunit 12 has a radio transmitter 16 and a receiver 18, and the basestation 14 has a radio transmitter 20 and a receiver 22. Thetransmitters 16, 20 and receivers 18, 22 are compatible for two-wayradio communication between the remote unit 12 and the base station 14.

[0081] In a preferred embodiment, the base station 14 includes aninterval timer 24 which causes the transmitter 20 to transmit atpredetermined intervals. The receiver 18 of the remote unit 12 receivesthe signal transmitted by the base station 14 and causes the transmitter16 to transmit a response to complete an electronic handshake.

[0082] The remote unit transmitter 16 is capable of transmitting at anenergy conserving lowpower level or at an emergency high-power level.When the distance between the remote unit 12 and the base station 14exceeds a predetermined limit, the remote unit responds at the higherpower level.

[0083] To accomplish the shift to the higher power level the remote unitreceiver 18 generates a signal 26 which is proportional to the fieldstrength of the received signal transmitted by the base station 14. Theremote unit 12 includes a comparitor 28 which compares the magnitude ofthe field strength signal 26 with a predetermined limit value 30 andgenerates a control signal 32.

[0084] The remote unit transmitter 16 is responsive to a circuit 34 forselecting transmission at either the low-power level or at thehigh-power level. The circuit 34 is connected to the control signal 32and selects transmission at the low-power level when the received fieldstrength equals or exceeds the limit value 30, and at the higher powerlevel when the received field strength is less than the limit value 30.Alternatively, the remote unit transmitter 16 transmits at one of aselectable plurality of transmission power levels. In anotheralternative embodiment, transmission is selectable within a continuousrange of transmission power levels.

[0085] Within an operating range of the personal alarm system 10, thefield strength of the base station 14 transmitted signal when receivedat the remote unit 12 is inversely proportional to the fourth power(approximately) of the distance between the two units. This distancedefines a ‘separation distance,’ and the predetermined limit value 30 isselected to cause transmission at the higher power level at a desiredseparation distance within the operating range.

[0086] In another embodiment, the remote unit 12 includes a hazardsensor 36 which is connected to the transmitter 16. The hazard sensor 36is selected to detect one of the following common hazards, waterimmersion, fire, smoke, excessive carbon monoxide concentration, andelectrical shock. In one embodiment, a detected hazard causes the remoteunit 12 to transmit a signal reporting the existence of the hazardouscondition at the moment the condition is detected. In anotherembodiment, the hazardous condition is reported when the response to theperiodic electronic handshake occurs.

[0087] In one embodiment, the base station 14 includes an audible alarm38 which is activated by the receiver 22. If the remote unit fails tocomplete the electronic handshake or reports a detected hazard orindicates it is out of range by sending an appropriate code, the basestation alarm 38 is activated to alert the operator.

[0088]FIG. 2 is a block diagram illustrating another embodiment of thepersonal alarm system of the present invention. The alarm system isindicated generally by the numeral 40 and includes a first remote unit42, a second remote unit 44 and a base station 46. The first remote unit42 includes a transmitter 48, a receiver 50, an identification number52, a received field strength signal 54, a comparitor 56, apredetermined limit value 58, a control signal 60, a power level selectcircuit 62 and a hazard sensor 64.

[0089] The second remote unit 44 includes a separate identificationnumber 66, but is otherwise identical to the first remote unit 42.

[0090] The base station 46 includes a transmitter 68, an interval timer70, a receiver 72, an alarm 74 and an ID-Status display 76.

[0091] In one embodiment of the invention illustrated in FIG. 2, theradio transmission between the first remote unit 42 and the base station46 includes the identification number 52. The transmission between thesecond remote unit 44 and the base station 46 includes theidentification number 66. It will be understood by those skilled in theart that the system may include one or more remote units, each having adifferent identification number 52.

[0092] It will also be understood that each remote unit 42 may have adifferent predetermined limit value 58. The limit value 58 defines adistance between the remote unit 42 and the base station 46 beyond whichthe remote unit will transmit at its higher power level. If a number ofremote units are being used to monitor a group of children, in a schoolplayground for example, the limit values of each remote unit may be setto a value which will cause high power transmission if the child wandersoutside the playground area. In other applications, the limit value 58of each remote unit 42 may be set to a different value corresponding todifferent distances at which the individual remote units will switch tohigh power transmission.

[0093] In one embodiment, the base station 46 will provide an alarm 74whenever a remote unit transmits at high power or reports the detectionof a hazard. The identification number of the reporting remote unit andan indication of the type of hazard is displayed by the base station onthe ID-Status display 76. This information can be used by the operator,for example a day-care provider, to decide what response is appropriateand whether immediate caretaker notification is required. If a child hasmerely wandered out of range, the provider may simply send an associateout to get the child and return her to the play area. On the other hand,a water immersion hazard indication should prompt immediate notificationof caretakers and emergency personnel and immediate action by theday-care employees.

[0094] In another embodiment, the remote unit receiver 50 determinesthat the separation distance between the remote unit 42 and the basestation 46 exceeds the predetermined threshold. The remote unittransmitter 48 transmits a code or status bit to indicate that fact.

[0095] In an embodiment illustrated in FIG. 1, the polling messagetransmitted periodically by the base station 14 is an RF carrier. Thecarrier frequency is transmitted until a response from the remote unit12 is received or until a watchdog timer (not illustrated) times out,resulting in an alarm The information contained in the remote unitresponse must include whether transmission is at low power or at highpower, and whether a hazard has been detected, since the base stationprovides an alarm in either of these instances.

[0096] In an embodiment illustrated in FIG. 2, however, additionalinformation must be reported and the advantages of a digitally formattedremote unit response will be apparent to those possessing an ordinarylevel of skill in the art.

[0097]FIG. 3 is a block diagram illustrating another embodiment of thepersonal alarm system in accordance with the present invention andgenerally indicated by the numeral 80. Personal alarm system 80 includesa remote unit 82 and a base station 84.

[0098] The remote unit 82 includes a transmitter 86, a receiver 88, apower level select circuit 90, an ID number 92, a visual beacon 94, anaudible beacon 96, a watchdog timer 98, a plurality of hazard sensors100 including a water immersion sensor 102, a smoke sensor 104, a heatsensor 106, a carbon monoxide sensor 108, a tamper switch 109, and anelectrical shock sensor 110, an emergency switch (“panic button”)112, abattery 113, and a ‘low battery power’ sensor 114.

[0099] The base station 84 includes a transmitter 116, a receiver 118which produces a received field strength signal 120, a comparitor 122, apredetermined limit value 124, a comparitor output signal 126, aninterval timer 128, control signals 130 and 132, a visual alarm 134, anaudible alarm 136, an ID and Status display 138, a circuit 140 forinitiating a phone call and a connection 142 to the public telephonesystem.

[0100] The base station 84 and a plurality of the remote units 82illustrated in the embodiment of FIG. 3 communicate using a digitallyformatted message. One message format is used by the base station 84 tocommand a specific remote unit 82, and a second message format is usedby a commanded remote unit 82 to respond to the base station 84. Thesemessage formats are illustrated in FIGS. 5 and 4, respectively.

[0101] With reference to FIG. 4 there is shown a pictorial diagram of apreferred digital format for a response from a remote unit in a personalalarm system in accordance with the present invention, indicatedgenerally by the numeral 150. The digital response format 150 includes aremote unit ID number 152, a plurality of hazard sensor status bits 154including a water immersion status bit 156, a smoke sensor status bit158, a heat sensor status bit 160, an excessive carbon monoxideconcentration status bit 162, and an electrical shock status bit 164.The response 150 also includes a high power status bit, 166, a panicbutton status bit 168, a low battery power detector status bit 170, atamper switch status bit 171, and bits reserved for future applications172.

[0102]FIG. 5 is a pictorial diagram of a preferred digital format for abase station to remote unit transmission, generally indicated by thenumeral 180. The digital message format 180 includes a command field 182and a plurality of unassigned bits 190 reserved for a futureapplication. The command field 182 includes a coded field of bits 184used to command a specific remote unit to transmit its response message(using the format 150). The command field 182 also includes a single bit186 used to command a remote unit, such as the embodiment illustrated inFIG. 3, to transmit at high power. The command field 182 includescommand bit 188 used to command a remote unit to activate a beacon, suchas the visual beacon 94 and the audible beacon 96 illustrated in FIG. 3.The command field 182 also includes command bit 189, used to command aremote unit to activate a GPS receiver, such as illustrated in FIG. 6.

[0103] In an alternative embodiment, the remote unit transmitter isadapted to transmit at one of a plurality of transmission power levelsand the single command bit 186 is replaced with a multi-bit commandsub-field for selection of a power level. In another embodiment, theremote unit transmitter is adapted to transmit at a power level selectedfrom a continuum of power levels and a multi-bit command sub-field isprovided for the power level selection.

[0104] Again with respect to FIG. 3, the Base station 84 periodicallypolls each remote unit 82 by transmitting a command 180 requiring theremote unit 82 to respond with message format 150. The polling isinitiated by the interval timer 128 which causes the base stationtransmitter 116 to transmit the outgoing message 180. The numerals 150and 180 are used to designate both the format of a message and thetransmitted message. A specific reference to the format or thetransmitted message will be used when necessary for clarity. As iscommon in the communications industry, the message will sometimes bereferred to as a ‘signal,’ at other times as a ‘transmission,’ and as a‘message;’ a distinction between these will be made when necessary forclarity.

[0105] The message 180 is received by all remote units and the remoteunit to which the message is directed (by the coded field 184) respondsby transmitting its identification number 152 and current status, bits154-170. The remote unit identification number 92 is connected to thetransmitter 86 for this purpose.

[0106] In the embodiment illustrated in FIG. 3, the function ofmeasuring received field strength to determine whether a predeterminedseparation distance is exceeded is performed in the base station 84. Thebase station receiver 118 provides a received field strength signal 120which is connected to the comparitor 122. The predetermined limit value124 is also connected to the comparitor 122 which provides a comparitoroutput signal 126. If the received field strength 120 is less than thelimit value 124, the comparitor output signal 126 is connected to assertthe “go-to-high-power” command bit 186 in the base unit 84 outgoingmessage 180. The limit value 124 is selected to establish thepredetermined separation distance beyond which transmission at highpower is commanded.

[0107] In one embodiment, the selection of the limit value 124 isaccomplished by the manufacturer by entering the value into a read-onlymemory device. In another embodiment, the manufacturer uses manuallyoperated switches to select the predetermined limit value 124. Inanother embodiment, the manufacturer installs jumper wires to select thepredetermined limit value 124. In yet another embodiment, the userselects a predetermined limit value 124 using manually operatedswitches.

[0108] The remote unit transmitter 86 is capable of transmitting at apower-conserving lower power level and also at an emergency higher powerlevel. Upon receiving a message 180 including the remote unitidentification number 184, the remote unit receiver passes the“go-to-high-power” command bit 186 to the power level select circuit 90which is connected to command the remote unit transmitter 86 to transmita response 150 at the higher power level. The response 150 includesstatus bit 166 used by the remote unit 82 to indicate that it istransmitting at high power.

[0109] In one embodiment, the remote unit includes the watchdog timer 98(designated a ‘No Signal Timeout’) which is reset by the receiver 88each time the remote unit 82 is polled. If no polling message 180 isreceived within the timeout period of the watchdog timer 98, the remoteunit transmitter 86 is commanded to transmit a non-polled message 150.

[0110] In one embodiment of the invention, the remote unit 82 includes amanually operated switch (“panic button”) 112 which is connected to thetransmitter 86 to command the transmission of a non-potted message 150.The panic button status bit 168 is set in the outgoing message 150 toindicate to the base station 84 that the panic button has beendepressed. Such a button can be used by a child or invalid or otherconcerned person to bring help.

[0111] In another embodiment, the remote unit includes a tamper switch109 which is activated if the remote unit is removed from the child, oris otherwise tampered with. The activation of the tamper switch 109causes the remote unit to transmit a code or status bit to the base unitto identify the cause of the change of status (‘Tamper’ status bit 171illustrated in FIG. 4). In one related alternative, the remote unittransmits at the higher power level when the switch is activated byremoval of the remote unit from the child's person.

[0112] In another embodiment, the remote unit 82 includes a circuit 114which monitors battery power. The circuit 114 is connected to initiate anon-polled message 150 if the circuit determines that battery power hasfallen below a predetermined power threshold. The message 150 willinclude the “low-battery-power” status bit 170. In an alternativeembodiment, a low battery power level will initiate a remote unittransmission at the higher power level (see FIG. 3).

[0113] In the embodiment illustrated in FIG. 3, the remote unit 82includes several hazard sensors 100. These sensors are connected toreport the detection of common hazards and correspond to the sensorstatus bits 154 in the remote unit response message 150.

[0114] In another embodiment of the present invention, the base stationreceiver 118 is connected to a visual alarm 134 and an audible alarm 136and will give an alarm when a message 150 is received which includes anyhazard sensor report 154 or any of the status bits 166-170.

[0115] The base station 84 also includes the status and ID display 138used to display the status of all remote units in the personal alarmsystem 80.

[0116] In another embodiment of the personal alarm system 80, the basestation 84 includes a circuit 140 for initiating a telephone call whenan emergency occurs. The circuit 140 includes the telephone numbers ofpersons to be notified in the event of an emergency. A connection 142 isprovided to a public landline or cellular telephone system. The circuit140 can place calls to personal paging devices, or alternatively placeprerecorded telephone messages to emergency personnel, such as thestandard “911” number.

[0117]FIG. 6 is a partial block diagram illustrating an embodiment ofthe invention having a base station 200 and at least one remote unit202. The partially illustrated remote unit 202 includes a transmitter204, hazard sensors 201, 203, 205, a circuit 208 for causing thetransmitter to transmit at a higher power level, a transmit intervaltimer 209, and a Global Positioning System (‘GPS’) receiver 210. Thepartially illustrated base station 200 includes a receiver 212, an alarm213, a display 214 for displaying global positioning coordinates oflongitude and latitude, a circuit 216 for converting the globalpositioning coordinates into predefined local coordinates, a map display218 for displaying a map in the local coordinates and indicating thelocation of the remote unit 202, and a watchdog timer 219.

[0118] In a preferred embodiment of the alarm system, the remote unittransmitter 204 is connected to receive the global positioningcoordinates from the GPS receiver 210 for transmission to the basestation 200.

[0119] The GPS receiver 210 determines its position and provides thatposition in global positioning coordinates to the transmitter 204. Theglobal position coordinates of the remote unit 202 are transmitted tothe base station 200. The base station receiver 212 provides thereceived global positioning coordinates on line 222 to display 214 andto coordinate converter 216. The display 214 displays the globalcoordinates in a world-wide coordinate system such as longitude andlatitude.

[0120] In one embodiment of the alarm system, the coordinate converter216 receives the global positioning coordinates from line 222 andconverts these into a preferred local coordinate system. A display 218receives the converted coordinates and displays the location of theremote unit 202 as a map for easy location of the transmitting remoteunit 202.

[0121] In another embodiment of the alarm system, the GPS receiver 210includes a low power standby mode and a normal operating mode. The GPSreceiver 210 remains in the standby mode until a hazard is detected andthen switches to the normal operating mode.

[0122] In another embodiment of the alarm system, the GPS receiver 210remains in the standby mode until commanded by the base station 200 toenter the normal operating mode (see command bit 189 illustrated in FIG.5).

[0123] In another embodiment of the alarm system, the remote unittransmitter 204 is connected to the hazard sensors 201-205 fortransmission of detected hazards. The base station receiver 212 isconnected to activate the alarm 213 upon detection of a hazard.

[0124] In one embodiment, a conventional electrical shock sensor 205includes a pair of electrical contacts 207 which are attached to theskin of a user for detection of electrical shock.

[0125] In another embodiment, the remote unit 202 includes a transmitinterval timer 209 and an ID number 211. The timer 209 is connected tocause the remote unit to transmit the ID number at predeterminedintervals. The base station 200 includes a watchdog timer 219 adapted toactivate the alarm 213 if the remote unit fails to transmit within theprescribed interval.

[0126] In another embodiment of the alarm system, the remote unit 202includes a carbon monoxide concentration sensor (see 108 of FIG. 3)having an output signal connected to activate a sensor status bit (see162 of FIG. 4) for transmission to the base station 200.

[0127] FIGS. 7-10 are pictorial illustrations of alternative embodimentsof the personal alarm system of the present invention. FIG. 7illustrates a base station 250 in two-way radio communication with aremote unit 252 worn by a child. The child is running away from the basestation 250 such that the separation distance 256 has exceeded thepreset threshold. The base station has determined that an alarm shouldbe given, and an audible alarm 254 is being sounded to alert aresponsible caretaker. FIG. 8 illustrates a remote unit worn at thewaist of a workman whose location and safety are being monitored. FIG. 9illustrates a mobile base station 270 equipped with a cigarette lighteradapter 272 for operation in a vehicle. FIG. 10 illustrates a basestation 280 adapted for operation from ordinary household current 282.

[0128]FIG. 11 is a block diagram which illustrates a man-over-boardsystem in accordance with one aspect of the present invention, anddesignated generally by the numeral 300.

[0129] The man-over-board system 300 includes a remote unit 302, havinga navigational receiver 304 and antenna 306 for receiving navigationalinformation, a sensor 308, having an output signal 310, a manuallyoperated switch 312, a radio transmitter 314 having an antenna 316. Theman-over-board system 300 also includes a base station 318 having aradio receiver 320 connected to an antenna 322 for receiving radiotransmissions from the remote unit 302. The base station 318 alsoincludes a display 324 for displaying the navigational location of theremote unit 302, a display 326 for displaying the status of the sensor308, a circuit 328 for comparing the field strength of the receivedradio transmission with a predetermined limit 330, and an alarm 332which is activated when the received field strength 334 falls below thevalue ofthe limit 330.

[0130] In use, the remote unit 302 is worn by a user and an alarm willbe given if the user falls over board and drifts too far from the boat.The navigational receiver 304 receives navigational information, as forexample from global positioning satellites 336. The navigationalreceiver 304 converts the navigational information into a location ofthe remote unit 302 and outputs the location 338 to the radiotransmitter 314 for transmission to the base station 318.

[0131] The sensor 308 provides an output signal 310 and defines a sensorstatus. The output signal 310 is connected to the radio transmitter 314for transmitting the sensor status to the base station 318.

[0132] The manually operated switch 312 includes an output 340 which isconnected to the radio transmitter 314 and permits the user to signalthe base station 318 by operating the switch 312. In a preferredembodiment, the manually operated switch 312 defines a panic button.

[0133] The radio receiver 320 provides three outputs, the receivedlocation 342 of the remote unit 302, the received sensor status 344, andan output signal 334 proportional to the field strength of the receivedradio transmission. As described above with respect to FIGS. 1-3, theremote unit 302 and the base station 318 define a separation distancewhich is inversely proportional to the received field strength. Thecomparitor circuit 328 compares the received field strength 334 with apredetermined limit 330 and produces an output signal 346 if the sign ofthe comparison is negative, indicating that the field strength of thereceived signal is less than the limit 330. If the user drifts beyond aseparation distance from the boat defined by the limit 330, the alarm332 is activated to alert the user's companions, who can then takeappropriate action.

[0134] In heavy seas or poor visibility, the base station 318 displaysthe current location of the remote unit 302 on a suitable display 324.This is done in some appropriate coordinate system, such as standardlongitude and latitude. This feature permits the base station tomaintain contact with the man-over-board despite failure to maintaindirect eye contact.

[0135]FIG. 12 is a block diagram which illustrates a man-over-boardsystem including a twoway radio communication link and designatedgenerally by the numeral 350. The man-over-board system 350 includes aremote unit 352 and a base station 354.

[0136] The remote unit 352 includes a navigational receiver 356, a radiotransmitter 358, a circuit 360 for causing the radio transmitter 358 totransmit at a high power level, a radio receiver 362, and circuits 364for activating a beacon.

[0137] The base station 354 includes a radio receiver 366, a radiotransmitter 368, a display 370 for displaying the location of the remoteunit 352, a compactor circuit 372, a predetermined limit 374, an alarm376, and control circuits 378 for activating the radio transmitter 368.

[0138] The navigational receiver 356 is connected to an antenna 380 forreceiving navigational information, such as from global positioningsystem satellites (not shown). The receiver provides the location 382 ofthe remote unit 352 for radio transmission to the base station 354.

[0139] The remote unit radio transmitter 358 and radio receiver 362 areconnected to an antenna 384 for communication with the base station 354.The base station radio receiver 366 and radio transmitter 378 areconnected to an antenna 386 for communication with the remote unit 352.

[0140] The base station radio receiver 366 provides two outputs, thelocation 388 of the remote unit for display by the location display 370,and a signal 390 whose value is inversely proportional to the fieldstrength of the signal received by the radio receiver 366.

[0141] The received field strength signal 390 and the predeterminedlimit 374 are compared by the comparitor circuit 372 to determinewhether the remote unit 352 is separated from the base station 354 by adistance greater than the predetermined limit 374. An alarm 376 is givenwhen the separation distance exceeds the limit.

[0142] The control circuits 378 are used to cause the radio transmitter368 to send a control signal to the remote unit 352 for selectinghigh-power remote unit radio transmission, or activating a visual oraudible beacon for use in locating the user in heavy seas or badvisibility.

[0143]FIG. 13 is a block diagram which illustrates an invisible fencefor monitoring a movable subject and designated generally by the numeral400. The invisible fence 400 includes a remote unit 402 and a basestation 404 in one-way radio communication.

[0144] The remote unit 402 includes a navigational receiver 406, a radiotransmitter 408, storage circuits 410 for storing information defining ageographical region, a comparitor 412, second storage circuits 414 forstoring information defining a predetermined positional status, an alarm416, and a circuit 418 and having a pair of electrical contacts 420, 422for providing a mild electrical shock.

[0145] The base station 404 includes a radio receiver 424, a comparitor426, storage circuits 428 for storing information defining apredetermined positional status, and an alarm 430.

[0146] In the embodiment illustrated in FIG. 13, the invisible fence 400defines a geographical region, for example the outer perimeter of anursing home in which elderly persons are cared for. If a particularpatient tends to wander away from the facility, creating an unusualburden upon the staff the remote unit 402 is attached to the patient'sclothing. If the patient wanders outside the defined perimeter, the basestation 404 alerts the staff before the patient has time to wander toofar from the nursing home.

[0147] Other applications are keeping a pet inside the yard, andapplying a mild electrical shock to the pet if it wanders too close to adefined perimeter. Attaching the remote unit 402 to a child and alertingthe caregiver in the event the child strays from a permitted area.Placing the remote unit around the ankle of a person on parole orprobation and giving an alarm if the parolee strays from a permittedarea. The invisible fence can also be used to monitor movement ofinanimate objects whose locations may change as the result of theft.

[0148] The remote unit navigational receiver 406 provides the location432 of the remote unit. In a preferred embodiment, the storage circuits410 are implemented using ROM or RAM, as for example within an embeddedmicroprocessor. Consideration of FIGS. 14-16 is useful to anunderstanding of how the invisible fence operates.

[0149]FIGS. 14, 15 and 16 are pictorial diagrams illustrating boundariesused to define geographical regions such as those used in a preferredembodiment of the invisible fence 400.

[0150]FIG. 14 shows a portion 440 of a city, including cross streets442-454 and a defining boundary 456. The boundary 456 divides the map440 into two portions, one portion above boundary 456, the other portionbelow.

[0151]FIG. 15 shows a portion 460 of a city, including cross streets(not numbered) and a closed boundary 462 made up of intersecting linesegments 464, 466, 468, 470, 472 and 474. The boundary 462 divides thecity map 460 into two subregions, one subregion defining an area 490wholly within the boundary 462, and the other subregion defining an area492 outside the boundary 462.

[0152]FIG. 16 shows a geographical region 480 which includes subregions482 and 484. Subregion 482 is entirely surrounded by subregion 484,while subregion 484 is enclosed within a pair of concentric closedboundaries 486 and 488.

[0153] The information which defines these geographical regions andboundaries is stored in the storage circuits 410, and serve as one inputto the comparitor 412 (FIG. 13). The conparitor 412 also receives thelocation output 432 from the navigational receiver 406. The comparitor412 compares the location of the remote unit 402 with the definedgeographical region and defines a relationship between the location andthe defined region which is expressed as a positional status. Thecomparitor 412 also receives an input from the second storage circuits414. These circuits store information defining a predeterminedpositional status.

[0154] Some examples will be useful in explaining how the positionalstatus is used. Referring to FIG. 14, remote unit locations 494 and 496are illustrated as dots, one location 494 being above the boundary 456,the other location 496 being below the boundary.

[0155] For the first example, assume that the location 494 is “within adefined geographical region,” and that the location 496 is “outside thedefined geographical region.” Assume also that the predeterminedpositional status is that “locations within the defined region areacceptable.” Next assume that the navigational receiver 406 reports thelocation 494 for the remote unit. Then the conparitor 412 will define apositional status that “the location of the remote unit relative to thedefined region is acceptable.” This positional status will betransmitted to the base station 404 and will not result in activation ofthe alarm 430.

[0156] For the next example, assume that that the navigational receiver406 reports the location of the remote unit to be the location 496, andthat the other assumptions remain the same. Then the comparitor 412 willdefine a positional status that “the location of the remote unitrelative to the defined region is not acceptable.” This positionalstatus will be transmitted to the base station 404 and will result inactivation of the alarm 430.

[0157] For the next example refer to FIG. 16 which includes threesuccessive locations 498, 500 and 502, shown linked by a broken line, asfor example by movement of the remote unit 402 from location 498 tolocation 500 to location 502. Assume that the area outside the boundary488 defines an “acceptable” subregion. Assume further that the areabetween the boundaries 488 and 486 defines a “warning” subregion. Alsoassume that the area 482 inside the boundary 486 defines a “prohibited”subregion. Finally, assume that the navigational receiver 406 providesthree successive locations 498, 500 and 502.

[0158] In a preferred embodiment, and given these assumptions in thepreceding paragraph, the comparitor 412 will determine that the location498 is acceptable and will take no further action. The comparitor 412will determine that the location 500 is within the warning subregion 484and will activate the remote unit alarm 416 to warn the person whosemovements are being monitored that he has entered a warning zone. Whenthe remote unit 402 arrives at the location 502, the comparitor 412 willdetermine that the remote unit has entered a prohibited zone and willactivate the mild electric shock circuit 418 which makes contact withthe skin of the monitored person through the electrical contacts 420,422. The positional status reported by the remote unit 402 for thesuccessive locations 498, 500 and 502 is “acceptable,” “warning given,”and “enforcement necessary,” respectively.

[0159] In another embodiment, no enforcement or warning are given by theremote unit 402. Instead, as when used to monitor the movements ofchildren or elderly patients, the positional status is transmitted tothe base station 404. There it is compared with a stored predeterminedpositional status and used to set an alarm 430 if the positional statusis not acceptable. The predetermined positional status is stored instorage circuits 428 and the comparison is made by the comparitor 426.

[0160] The preferred embodiment for the storage and comparison circuitsis the use of an embedded microprocessor.

[0161]FIG. 17 is a block diagram illustrating a personal alarm systemsuch as the invisible fence of FIG. 13, and designated generally by thenumeral 520. Personal alarm system 520 includes a remote unit 522 and abase station 524.

[0162] The remote unit 522 includes a radio transmitter 526 and a radioreceiver 528 connected to a shared antenna 530. The base station 524includes a radio receiver 532 and a radio transmitter 534 connected to ashared antenna 536 and defining a two-way communication link with theremote unit 522.

[0163] In one preferred embodiment, the communication link is directbetween the respective transmitters 526, 534 and the correspondingreceivers 528, 532. Other embodiments include access to existingcommercial and private communications networks for completing thecommunication link between the remote unit 522 and the base station 524.Typical networks include a cellular telephone network 538, a wirelesscommunications network 540, and a radio relay network 542.

[0164]FIG. 18 is a block diagram showing an environmental monitoringsystem for use in fixed locations, designated generally by the numeral550. The environmental monitoring system 550 includes a remote unit 552and a base station 554.

[0165] The remote unit 552 includes storage circuits 556 for storinginformation defining the location of the remote unit 552, at least onesensor 558, a radio transmitter 560, and an antenna 562.

[0166] The base station 554 includes an antenna 564, a radio receiver566, a display 568 for displaying the location of the remote unit 552, acomparitor 570, storage circuits 572 for storing information defining apredetermined sensor status, and an alarm 574.

[0167] The environmental monitoring system 550 is useful forapplications in which the remote unit 552 remains in a fixed locationwhich can be loaded into the storage circuits 556 when the remote unit552 is activated. Such applications would include use in forests forfire perimeter monitoring in which the sensor 558 was a heat sensor, orin monitoring for oil spills when attached to a fixed buoy and thesensor 558 detecting oil. Other useful applications include anyapplication in which the location is known at the time of activation andin which some physical parameter is to be measured or detected, such assmoke, motion, and mechanical stress. The environmental monitoringsystem 550 offers an alternative to pre-assigned remote unit ID numbers,such as those used in the systems illustrated in FIGS. 2 and 3.

[0168] The storage circuits 556 provide an output 576 defining thelocation of the remote unit 552. This output is connected to the radiotransmitter 560 for communication with the base station 554. The sensor558 provides an output signal 578 defining a sensor status. The outputsignal is connected to the radio transmitter 560 for communication ofthe sensor status to the base station 554.

[0169] The communications are received by the base station's radioreceiver 566 which provides outputs representing both the location 580of the remote unit 552 and the sensor status 582. The location 580 isconnected to the display 568 so that the location of the remote unit 552can be displayed. The comparitor 570 receives the sensor status 582 andthe information defining the predetermined sensor status which is storedin the storage circuits 572. If the comparitor 570 determines that thesensor status indicates an alarm situation, it activates the alarm 574to alert a base station operator.

[0170]FIG. 19 is a block diagram which illustrates an alternativeembodiment of a personal alarm system in which the remote unit transmitsdemodulated navigational and precise time-of-day information to the basestation, and the base station uses that information to compute thelocation of the remote unit. This alternative embodiment is designatedgenerally by the numeral 600 and includes a remote unit 602 and a basestation 604.

[0171] The remote unit 602 includes a navigational receiver 606, ademodulator circuit 608, a precise time-of-day circuit 610, a sensor612, and a radio transmitter 614.

[0172] The base station 604 includes a radio receiver 616, computationalcircuits 618 for computing the location of the remote unit 602, adisplay 620 for displaying the computed location, a second display (canbe part of the first display) 622 for displaying a sensor status, acomparitor 624, storage circuits 626 for storing information defining apredetermined sensor status, and an alarm 628.

[0173] In a preferred embodiment, the navigational receiver 606 receivesnavigational information from global positioning system satellites (notshown). In this embodiment, the raw navigational information isdemodulated by the demodulator circuit 608 and the output of thedemodulator 608 is connected to the radio transmitter 614 forcommunication to the base station 604.

[0174] The precise time-of-day circuits 610 provide the time-of-dayinformation needed to compute the actual location of the remote unitbased upon the demodulated navigational information. In the case of GPSnavigational information, geometric dilution of precision computationsare done at the base station 604 to derive the actual location of theremote unit 602.

[0175] The sensor 612 provides an output signal defining a sensorstatus. The demodulated navigational information, the precisetime-of-day information and the sensor status are all connected to theradio transmitter 614 for communication to the base station 604.

[0176] At the base station 604, the radio receiver 616 provides thenavigational and precise time-of-day information to the computationcircuits 618 for determining the actual location. In a preferredembodiment, the computation is made using an embedded microprocessor.The computed location is displayed using the display 620.

[0177] The radio receiver 616 also provides the received sensor statuswhich forms one input to the comparitor 624. Stored information defininga predetermined sensor status is provides by the storage circuits 626 asa second input to the comparitor 624. If the received sensor status andthe stored sensor status do not agree, the comparitor 624 activates thealarm 628 to alert the base station operator.

[0178]FIG. 20 is a block diagram which illustrates an alternativeembodiment of the invisible fence system in which the base stationcomputes the location of the remote unit, and in which the fencedefinitions are stored at the base station rather than in the remoteunit. The alternative system is designated generally by the numeral 650and includes a remote unit 652 and a base station 654.

[0179] The remote unit 652 includes a navigational receiver 656, ademodulator circuit 658, a precise time-of-day circuit 660, a radiotransmitter 662, a radio receiver 664, a shared antenna 666, and controlstatus circuits 668.

[0180] The base station 654 includes a radio receiver 670, a radiotransmitter 672, a shared antenna 674, computation circuits 676, storagecircuits 678, second storage circuits 680, a first comparitor 682, asecond comparitor 684, a display 686, an alarm 688, and control circuits690.

[0181] The navigational receiver 656 provides raw navigationalinformation 692 to the demodulator circuit 658. The demodulator circuit658 demodulates the raw navigational information and providesdemodulated navigational information 694 to the radio transmitter 662for communication to the base station 654. The precise time-of-daycircuit 660 provides time-of-day information 696 to the radiotransmitter 662 for communication to the base station 654.

[0182] The base station radio receiver 670 provides receivednavigational information 698 and received time-of-day information 700 tothe computation circuits 676 for conversion to an actual location 702 ofthe remote unit 652. The storage circuits 678 store information defininga geographical region.

[0183] The first comparitor 682 receives the location 702 and the regiondefining information 704 and provides a positional status 706, asdescribed above with respect to FIGS. 13-16.

[0184] The second storage circuits 680 store information 708 defining apredetermined positional status. The second comparitor 684 receives thepositional status 706 and the predetermined positional status 708 andprovides control output signals 710 based upon the results of thepositional status comparison. When the location 702 is within a defined“warning” or “restricted” zone, the second comparitor 684 activates thealarm 688 and causes the location 702 to be displayed by the display686.

[0185] In one preferred embodiment, the remote unit includes circuits668 which provide a means by which the base station 654 can warn theremote unit user or enforce a restriction, as for example, by applyingthe mild electric shock of the embodiment shown in FIG. 13. The secondcomparitor 684 uses a control signal 710 to activate the controlcircuits 690 to send a command via the radio transmitter 672 to theremote unit 652 for modifying the remote unit control status. Forexample, if the remote unit location is within a restricted zone, thebase station 654 will command the remote unit 652 to provide an electricshock to enforce the restriction.

[0186]FIG. 21 is a block diagram illustrating another embodiment of aman-over-board alarm system, designated generally by the numeral 750.The man-over-board alarm system 750 includes a remote unit 752 and abase station 754.

[0187] The remote unit 752 includes a navigational receiver 756, a radiotransmitter 758, an environmental sensor 760, at least one manuallyoperated switch 762, a beacon 764, a circuit 766 for activating thenavigational receiver 756, and a control circuit 768.

[0188] The base station 754 includes a radio receiver 770, a remote-unitlocation display 772, a sensor status display 774, an alarm 776, aswitch status display 778, a control circuit 780, and storage 782 for apredetermined limit value.

[0189] The navigational receiver 756 receives navigational informationvia an antenna 757 and provides a location 759 of the remote unit to theradio transmitter 758 for transmitting the remote unit location 759. Thenavigational receiver 756 has a normal operational mode and a low-powerstandby mode. In a preferred embodiment, the navigational receiver 756is normally in the low-power standby mode, thereby conserving operatingpower which is normally supplied by batteries.

[0190] The circuit 766 is responsive to the control circuit 768 forselecting the operational mode and thereby “activating” the navigationalreceiver. In a specific embodiment, the control circuit 768 isresponsive to a hazard sensor 760, such as a water-immersion sensor, forcontrolling the circuit 766 to activate the navigational receiver 756.In another embodiment, the control circuit 768 is responsive to amanually operated switch 762, such as a manually operated panic button,for activating the navigational receiver 756.

[0191] In a specific embodiment, the sensor 760 provides an outputsignal 761, and defines a sensor status. The manually operated switch762 provides an output signal 763, and defines a switch status. Thecontrol circuit 768 receives the sensor output signal 761 and the switchoutput signal 763, and connects each to the radio transmitter 758 forcommunication of the sensor status and the switch status to the basestation 754.

[0192] In another specific embodiment, the control circuit 768 isconnected for activating the remote unit beacon 764 in response to achange in the sensor status 761. In another embodiment, the controlcircuit 768 activates the beacon 764 in response to a change in theswitch status 763. In one embodiment, the beacon 764 is a visual beacon,such as a flashing light. In another embodiment, the beacon 764 is anaudible beacon which emits a periodic sound. The beacon 764 aidssearchers in locating a man-over-board.

[0193] In a specific embodiment, the control circuit 768 is implementedusing a programmed micro-processor. In another specific embodiment, thecontrol circuit 768 is implemented using an imbedded, programmedmicro-processor. In another embodiment, the control circuit 768 isimplemented using a programmed micro-controller.

[0194] The base-station radio receiver 770 receives the remote unitlocation 759, the sensor status, and the switch status. The radioreceiver 770 is connected to the display 772 for displaying the receivedremote unit location, is connected to the display 774 for displaying thereceived sensor status, and is connected to the display 778 fordisplaying the switch status. In a specific embodiment, the radioreceiver 770 is connected to the alarm 776 which is activated by achange in the sensor status, such as the detection of immersion inwater. In another specific embodiment, the alarm is activated by achange in the switch status, such as a manual operation of the panicbutton.

[0195] The radio receiver 770 provides a signal 771 corresponding to afield strength of a received radio communication. The control circuit780 compares the received field strength 771 with a predetermined limitvalue 783 provided by circuit 782. The control circuit 780 is connectedto activate the alarm 776 when the received field strength is less thanthe predetermined limit value 783. The received field strength 771, thecontrol circuit 780, and the predetermined limit value 783 define aseparation distance between the remote unit 752 and the base station754, as discussed above with respect to other embodiments of theinvention.

[0196] In a specific embodiment, the control circuit 780 and the circuit782 for providing the predetermined limit value 783 are implementedusing a programmed micro-controller. In another specific embodiment, thecircuit 780 and the circuit 782 are implemented using an embedded,programmed micro-controller. The functions performed by the circuits 780and 782 are performed in different embodiments alternatively by discreteintegrated circuits, by a programmed micro-controller, by an embedded,programmed micro-controller, by a programmed micro-processor, and by anembedded, programmed micro-processor.

[0197] In a specific embodiment of the man-over-board alarm systemillustrated in FIG. 21, the sensor 760 includes a plurality ofenvironmental, physiological and hazard sensors providing output signalsand defining a sensor status vector. In another specific embodiment, thesensor 760 provides a plurality of output signals 761 defining anotherstatus vector. In another specific embodiment, the sensor 760 providesan analog output signal 761, and the control circuit 768 converts theanalog signal 761 for radio transmission as a sensor status vector. Thebase station 754 displays the sensor status vector using the display774.

[0198] In another specific embodiment of the man-over-board alarm systemillustrated in FIG. 21, the manually operated switch 762 includes aplurality of manually operated switches providing multiple outputsignals 763. The multiple output signals 763 define a switch statusvector which is connected to the control circuit 768 for radiotransmission to the base station 754. The base station 754 displays theswitch status vector using the display 778. In a specific embodiment,the remote unit manually operated switches 762 define a numeric keypad,and the base station 754 displays a manual entry made using the numerickeypad. In another specific embodiment, the manually operated switches762 define an alpha numeric keypad, and the base station 754 displaysmanually entered alpha numeric information.

[0199]FIG. 22 is a partial block diagram of the man-over-board alarmsystem illustrated in FIG. 21, and designated generally by the numeral800. The alarm system 800 includes a remote unit 802 and a base station804. The remote unit 802 includes a radio transmitter 806 and amicrophone 808. The base station 804 includes a radio receiver 810 and aspeaker 812. In this embodiment of the alarm system 800, the microphone808 is connected to the transmitter 806 for defining a one-way voiceradio communication channel with the base station receiver 810 andspeaker 812. In a specific embodiment, the radio transmitter 806 is alsoused to transmit the remote unit location, the sensor status vector, andthe switch status vector as discussed above with respect to FIG. 21. Inanother specific embodiment, the radio receiver 810 is also used toreceive the remote unit location, the sensor status vector, the switchstatus vector, and to provide the received signal strength signal.

[0200]FIG. 23 is also a partial block diagram of the man-over-boardalarm system shown in FIG. 21. The alarm system is designated generallyby the numeral 814. The alarm system 814 includes a remote unit 816 anda base station 818. The remote unit 816 includes a radio transmitter820, a microphone 822, a radio receiver 824 and a speaker 826. The basestation 818 includes a radio receiver 828, a speaker 830, a radiotransmitter 832 and a microphone 834. These elements are configured toprovide a two-way voice communication channel between the remote unit816 and the base station 818. In a specific embodiment, the radiotransmitter 820 and radio receiver 828 are also used to communicate theremote unit location, the sensor status vector, and the switch statusvector. In another specific embodiment, the radio receiver 828 alsoprovides a received signal strength signal FIG. 24 is a block diagramillustrating another embodiment of an invisible fence system, designatedgenerally by the numeral 850. The invisible fence system 850 includes aremote unit 852 and a base station 854.

[0201] The remote unit 852 includes a navigational receiver 856, a radiotransmitter 858, a memory 860 for storing information defining ageographic region, a memory 862 for storing information defining apredetermined positional and time status, a circuit 863 for providingtime-of-day information, a comparison circuit 864, and an enforcementand alarm circuit 865.

[0202] The base station 854 includes a radio receiver 866, a memory 868for storing a predetermined positional and time status, a comparisoncircuit 870 and an alarm 872.

[0203] The invisible fence system illustrated in FIG. 24 differs fromthe embodiment of FIG. 13 by providing an alarm and enforcement basedupon both time and location. The embodiment of FIG. 24 allows thedefining of zones of inclusion, and alternatively zones of exclusion,which are defined in terms of location and time-of-day. For example, aparolee equipped with the remote unit 852 may be confined to, andalternatively excluded from, a defined region between the hours of 6 PMand 6 AM. If the parolee leaves the region of confinement, or enters theregion of exclusion, between those two time limits, a radio transmissionactivates the alarm 872 at the base station 854, and simultaneouslyactivates an alarm and enforcement process 865 at the remote unit 852.In a specific embodiment, the parolee is first warned that he has left aregion of confinement at an unallowed time. If the violation continues,the parolee is given a mild electrical shock. If the violationcontinues, the intensity of the electrical shock is increased. Theauthorities are put on notice by the base station alarm 872 that theparolee has violated his defined restrictions.

[0204]FIG. 25 is a pictorial diagram illustrating boundaries used todefine geographical regions such as those used in a preferred embodimentof the invisible fence system 850. FIG. 25 shows a portion 1000 of acity, including cross streets (not numbered) and a closed boundary madeup of intersecting line segments 1006, 1008, 1010 and 1012. The boundarydivides the city map 1000 into two subregions, one subregion defining anarea 1002 wholly within the boundary, and the other subregion definingan area 1004 outside the boundary.

[0205] In a specific embodiment of an invisible fence system, such asthat illustrated in FIG. 24, a memory 860 stores information defining ageographical region, for example the region 1002. In an example of theoperation of the specific embodiment, assume the region 1002 representsa specific city block, surrounded by the city streets 1006, 1008, 1010and 1012. Further assume that a parolee is wearing the remote unit 852,and that the parolee is required by the terms of his parole to remainwithin the city block 1002 between the hours of 8 PM and 7 AM, and thatat all other times the parolee is permitted to be outside the region1002.

[0206]FIG. 26 is a table defining a relationship between the location ofthe remote unit 852 (FIG. 24) and the time-of-day for use inunderstanding a curfew feature of a specific embodiment of the invisiblefence system 850. Each row of the table represents a different location,and each column of the table represents a subdivision of thetime-of-day. The relationship defined by the table represents an exampleof a curfew requiring the parolee (in the preceding example) to remainat home, i.e., within the city block 1002, between 8 PM and 7 AM. If theparolee leaves home during the interval from 8 PM to 7 AM, an alarm 872is activated at the base station 854. The information represented by thetable is stored in a memory 862 in the remote unit 852, and is referredto as a ‘predetermined positional and time status.’

[0207] With respect to the specific embodiment illustrated in FIG. 24,the memory 860 stores information defining the geographical region 1002(FIG. 25). The comparison circuit 864 receives the remote unit location859, the time-of-day 861, the information defining the geographicalregion 1002, and the curfew defining information 867. The comparisoncircuit 864 compares the named items of information and provides apositional and time status 869 to the radio transmitter 858 forcommunication to the base station 854. In another embodiment of theinvisible fence system 850, the transmitter 858 periodically transmitsthe remote unit location 859 and time-of-day 861. This information isreceived at the base station 854 where the predetermined positional andtime status is stored in a memory 868. The base station 854 makes anindependent determination of whether or not the curfew is violated. Thepositional and time status is compared by circuit 870 with the receivedlocation and time-of-day information. An alarm 872 is given if theremote unit violates the established curfew.

[0208]FIG. 27 is a block diagram illustrating another embodiment of aninvisible fence system, designated generally by the numeral 1020. Theinvisible fence system 1020 includes a remote unit 1022 and a basestation 1024. The remote unit 1022 includes a navigational receiver1026, a radio transmitter 1028, a radio receiver 1030 and an enforcementand alarm circuit 1032. The base station 1024 includes a radio receiver1034, a radio transmitter 1036, a memory 1040 for storing informationdefining a geographical region, a memory 1042 for storing informationdefining a predetermined positional and time status, a display 1044 andan alarm 1046.

[0209] The navigational receiver 1026 provides information 1027 defininga location of the remote unit 1022, and is connected to the remote unitradio transmitter 1028 for communicating the remote unit location to thebase station 1024. The transmitted remote unit location is received bythe base station radio receiver 1034 and provided on line 1035 to thecontrol/compare circuit 1038. The base station includes a circuit 1037for providing time-of-day information 1039 to the control/comparecircuit 1038.

[0210] In a specific embodiment, the control/compare circuit 1038 isimplemented as part of a programmed, imbeddedmicro-processor/micro-controller. A memory of the imbeddedmicro-processor provides the memory 1040 for storage of information 1041defining a geographical region, and the memory 1042 for storage ofinformation 1043 defining a predetermined positional and time status.The imbedded micro-processor implementation of the control/comparecircuit 1038 receives the remote unit location 1035, the time-of-day1039, the information 1041 defining a geographical region, and theinformation 1043 defining a predetermined positional and time status.

[0211] In the previous example, the defined geographical regioncorresponded to the region 1002 (FIG. 25), and the predeterminedpositional and time status corresponded to the relationship defined bythe table in FIG. 26. The parolee was required to be within the region1002 between the hours of 8 PM and 7 AM. The compare/control circuit1038 compares the received information described above and determineswhether the parolee is in violation of the defined curfew. The paroleeis in violation of the curfew defined by the table in FIG. 26 when he isoutside his home between the hours of 8 PM and 7 AM. In this example,the region 1002 (FIG. 25) corresponds to the parolee's home. Locationsoutside region 1002 are therefore outside his home. In this example, ifthe parolee is in violation of the curfew, the control/compare circuit1038 generates a signal 1045, connected to the base station radiotransmitter 1036 for activating an alarm/enforcement device 1032 at theremote unit 1022. Such a device and an alarm/enforcement protocol havebeen described above with respect to FIG's 13 and 16.

[0212] In a specific embodiment of the invisible fence system shown inFIG. 27, the location of the remote unit is displayed 1044 at the basestation 1024. In one embodiment, the control/compare circuit 1038continuously displays the remote unit location. In another embodiment,the control/compare circuit 1038 provides and alarm 1046 and displaysthe remote unit location when the parolee has violated the curfew.

[0213] In a specific embodiment of the invisible fence system of FIG.27, the time-of-day circuit 1037 is implemented as part of the imbeddedmicro-processor. When several remote units are transmitting theirlocations from different time zones, the base station time-of-day isadjusted at the base station to use the correct time-of-day for eachtransmitting remote unit. For a curfew type process, it is not necessarygenerally to use a precise time-of-day. However, when a precisetime-of-day is required, the remote unit transmitter is connected toreceive both a location and a precise time-of-day from the navigationalreceiver, or other precise time-of-day circuit, for transmission to thebase station. Such arrangements are illustrated in FIG's 19, 20, 34 and36.

[0214]FIG. 28 is a partial block diagram illustrating an alarm system,designated generally by the numeral 1050. The alarm system 1050 includesa remote unit 1052 and a base station 1054 and is intended to berepresentative of many of the alarm systems in accordance with aspectsof this invention. The remote unit 1052 includes a radio transmitter1056 and a radio receiver 1058. The base station 1054 includes a modem1060. Through its modem 1060, the base station 1054 is connected to astandard communications channel, designated 1064 and a two-way radiolikn 1062, permitting a two-way communication between the base station1054 and the remote unit 1052.

[0215] Such an arrangement provides a radio link for communicating withthe remote unit 1052 while not requiring the base station 1054 toinclude the necessary radio receiver and radio transmitter. In such acase, the base station includes a communications receiver and acommunications transmitter which in one embodiment includes a radiocommunications facility and in another embodiment provides the modem capability. The modem 1060 permits the base station to be connected viastandard land line communications, such as a commercial telephonenetwork. Thus the standard communication channel 1064 includes astandard telephone network, communications satellites, relay type radiolinks and other common carrier technologies such as cellular telephone,wireless communications, and personal communications systems (“PCS”).

[0216]FIG. 29 is a partial block diagram illustrating an alternativeembodiment of the personal alarm system 80 as depicted in FIG. 3. Partsshown in FIG. 29 which correspond to parts shown in FIG. 3 have the sameidentification numerals.

[0217]FIG. 29 illustrates a radio transmitter 86, a circuit 90 forselecting a transmission power level for the transmitter 86. Anoil/chemical sensor 113 is added to the hazard sensors 100. Each sensorprovides an output signal defining a sensor status. The sensor status ofall sensors is connected via a line 111 to the transmitter 86 fortransmission of the sensor status. The output of each sensor 100 isconnected via line 117 to the selection circuit 90 for selecting atransmission power level. The transmitter 86 normally operates at areduced power level to conserve battery power. When a hazard sensor 100detects a hazardous condition, the line 117 communicates that fact tothe circuit 90 which causes the transmitter 86 to transmit at a higherpower level.

[0218]FIG. 30 is a block diagram illustrating a specific embodiment of apersonal alarm system, designated generally by the numeral 1080, andincluding a remote unit 1082 and a base station 1084. The remote unit1082 includes a radio transmitter 1086, a radio receiver 1088, a controlcircuit 1090, a transmission power level selection circuit 1092 and asensor 1094. The base station 1084 includes a radio receiver 1096, aradio transmitter 1098, an alarm 1100 and a higher power level commandcircuit 1102.

[0219]FIG. 30 illustrates a system in which a sensor status 1095 istransmitted to the base station 1084 and generates an alarm 1100. Thecommand circuit 1102 is responsive to the received sensor status andcauses the base station transmitter 1098 to transmit a command to theremote unit 1082 causing the remote unit to transmit at a higher powerlevel. The command is received by the remote unit receiver 1088 and isinterpreted by the control circuit 1090 to select a higher powertransmission level 1092.

[0220]FIG. 31 is a partial block diagram illustrating a circuit 1130including an analog-to-digital converter 1132 and a read-only memory1134. The analog-to-digital converter 1132 receives an analog inputsignal 1131 and provides digital output signals 1133. The digital outputsignals 1133 are connected to address input lines of theread-only-memory 1134. The read-only-memory provides digital outputsignals of stored information from an addressed memory location onoutput lines 1135.

[0221] The circuit shown in FIG. 31 is used to convert a received fieldstrength signal, such as signal 771 in the base station 754 of FIG. 21,to a predetermined digital output vector on lines 1135.

[0222]FIG. 32 is a partial block diagram illustrating adigital-to-analog converter 1140. The digital-to-analog converter 1140receives digital input signals on lines 1141 and provides an analogoutput signal on line 1142.

[0223]FIG. 33 is a block diagram illustrating an embodiment of apersonal alarm system, designated generally by the numeral 1150, andincluding a remote unit 1152 and a base station 1154. The remote unit1152 includes a radio transmitter 1156, a radio receiver 1158, a circuit1160 for selecting transmission power level and a sensor 1162. The basestation 1154 includes a radio receiver 1164, a radio transmitter 1166,an alarm 1168 and a command control circuit 1170. The digital-to-analogconverter illustrated in FIG. 32 is used in a specific embodiment of thecircuit 1160 of FIG. 33 for selecting one of a plurality of transmissionpower levels, as commanded by the base station. The base stationreceiver 1164 provides a signal 1165 proportional to a received fieldstrength. In a specific embodiment, the signal 1165 is an analog signaland is converted to a digital form using the conversion circuit 1130 ofFIG. 31. The digital output signals 1135 are used by the command controlcircuit 1170 to generate a power-level command 1171 for transmission tothe remote unit 1152. In one embodiment of the remote unit select powerlevel circuit 1160, the received digital powerlevel command is useddirectly to control the power level of the remote unit transmitter 1156.In another embodiment, the received power-level command is converted toan analog signal which is used to control the power level of the remoteunit transmitter 1156. In this manner, the alarm system is able tocompensate for an increase in separation distance, low remote unitbattery power or other conditions which cause the received signalstrength 1165 to be reduced. The circuits are also able to command areduction of the remote unit transmitting power level to conserve remoteunit battery power.

[0224]FIG. 34 is a block diagram illustrating a specific embodiment of aweather alarm system, designated generally by the numeral 1180. Theweather alarm system 1180 includes a remote unit 1182 and a base station1184.

[0225] The remote unit 1182 includes a navigational receiver 1186, aweather receiver 1188, a radio transmitter 1190, region definingcircuits 1192, weather threshold defining circuits 1194, informationcombining circuits 1196, and information comparison circuits 1198.

[0226] The base station 1184 includes a radio receiver 1200, a displaycircuit 1202, and an alarm 1204.

[0227] The weather alarm system 1180 operates generally as follows, theremote unit 1182 is deployed in the field, such as in a small, privateaircraft and is used to monitor the weather within a zone surroundingthe aircraft. As the aircraft moves, the zone surrounding the aircraftmoves also. A navigational receiver 1186 is used to determine thelocation of the aircraft at any point in time. A weather receiver 1188receives weather parameters broadcast by a Weather Surveillance RadarSystem of the U.S. Weather Service, providing up-to-date weatherinformation for the United States. The remote unit is programmed tomonitor specific weather parameters within the zone surrounding theaircraft and to compare those parameters with programmed limits. In theevent that one or more of the monitored parameters exceeds theprogrammed limit, the remote unit transmitter 1190 is activated andtransmits the location 1187 of the aircraft. In some embodiments,specific weather parameters are also transmitted. The base station 1184receives the transmission, displays 1202 the location and anytransmitted weather parameters, and, if appropriate, gives an alarm1204.

[0228]FIG. 35 is a pictorial diagram illustrating an example of aweather region useful in understanding the operation of the weatheralarm system 1180 and similar embodiments. The weather region isdesignated generally by the numeral 1220 and 1220 includes a region 1222in which weather parameters are received from a weather surveillanceradar system. Within the region 1222 is a weather alarm system remoteunit at a moving location 1224 and surrounded by a moving zone 1226having a constant radius 1228. It is perhaps more relevant to state thatat any point in the contiguous 48 states of the lower continental UnitedStates the weather receiver 1188 receives weather parameters relevant tothe current location 1224 of the weather alarm system remote unit 1182(the aircraft, in our example above). The aircraft is surrounded by amoving zone 1226 and the remote unit is monitoring specified weatherparameters within the moving zone, notifying the base station 1184 whenany monitored parameter exceeds its programmed limit.

[0229]FIG. 36 is a pictorial diagram illustrating an example of anotherweather region, designated generally by the numeral 1240. In thisexample, the weather region 1240 includes an area of weather reporting1242. The aircraft is located at point 1244 and is moving in a directionand at a velocity shown by a vector 1246. In this example, the definedzone of weather parameter monitoring is 1248.

[0230] With respect once again to FIG. 34, the remote unit circuits 1192are used to define the zone (1226 in FIG. 35, and 1248 in FIG. 26) whichis moving relative to the aircraft. In a specific embodiment, thecircuits 1192 are a memory portion of a programmed microcontroller, andthe zone is defined by information stored in the memory portion. Thedefined zone is designated by the numeral 1193.

[0231] The remote unit circuits 1194 define specific weather parametersto be monitored and also define specific threshold values, limits andranges for use in monitoring the weather parameters. The defined valuesare designated generally by the numeral 1195 and in a specificembodiment are stored in a memory portion of a programmedmicro-controller.

[0232] As the aircraft proceeds on its flight, the navigational receiver1186 continues to provide a current location 1187, while the weatherreceiver 1188 continues to provide current weather information 1189. Thelocation 1187 and the surrounding zone defining information 1193 arecombined by circuits 1196 and define a zone relative to the weatherreporting region (1222 in the example of FIG. 35, and 1242 in theexample of FIG. 36). This relative zone is compared by circuits 1198with the received weather parameters 1189 and the selected weatherparameters and limit values 1195 to determine whether or not anymonitored parameter within the moving zone exceeds it limit. The line1199 is used to activate the remote unit transmitter 1190 fortransmitting the current location 1187 and the result 1199 of thecomparison.

[0233]FIG. 37 is a partial block diagram illustrating a specificembodiment of a remote unit for a weather alarm system. The portion ofthe remote unit is designated generally by the numeral 1250, andincludes a navigational receiver 1252, a circuit 1254 for defining anactivation threshold, and a comparison circuit 1256. In the embodimentillustrated here, received weather parameters 1258 are compared withlimit values, threshold values and ranges stored in the circuit 1254. Ifany specified weather parameter exceeds its individual limit value, thecomparison circuit 1256 activates the navigational receiver 11252 whichhas been operating in a standby mode. Since current location is notavailable until the navigational receiver is activated, the receivedweather parameters 1258 are not limited to a moving zone around theaircraft, but apply to the entire weather reporting region (1222 in theexample of FIG. 35, and 1242 in the example of FIG. 36). In a specificembodiment, the circuits 1254 and 1256 are part of a programmedmicro-controller.

[0234]FIG. 38 is a block diagram of another specific embodiment of aweather alarm system, designated generally by the numeral 1270. Theweather alarm system 1270 includes a remote unit 1272 and a base station1274.

[0235] The remote unit 1272 includes only a navigational receiver 1276,providing a current location to a radio transmitter 1278 fortransmission to a base station.

[0236] The base station 1274 includes a radio receiver 1280 forreceiving the current location 1281, a weather receiver 1282 forreceiving weather parameters, a region defining circuit 1284 fordefining a zone relative to the current remote unit location, a weatherthreshold defining circuit 1286 for selecting specific weatherparameters and for defining limits, thresholds, and ranges for the eachselected weather parameter, an information combining circuit 1288 forcombining the current location and the zone defining information, acomparison circuit 1290 for selecting the specified parameters withinthe zone relative to the current location, comparing the selectedparameters within the zone with their individual limits, and activatingan alarm 1294 and displaying 1292 the current location and comparisonresults when a monitored weather parameter within the defined distanceof the remote unit exceeds its limit, falls below its defined threshold,and falls inside/outside of a defined range.

[0237] In the embodiment illustrated in FIG. 38 all the intelligence isplaced into the base station 1274, including the weather receiver 1282.In a specific embodiment, the circuits 1284, 1286, 1288 and 1290 arepart of a programmed micro-controller.

[0238]FIG. 39 is a block diagram illustrating a self-locating remotealarm unit designated generally by the numeral 1300. The remote unit1300 includes a circuit 1302 defining a first variable and providing avalue 1303 for the first variable, a circuit 1304 defining a secondvariable and providing a value 1305 for the second variable, acommunications transmitter 1306, a circuit 1308 defining a condition andproviding a value for the condition, a circuit 1310 for comparing thevalue of the first variable with the value of the condition, and acircuit 1312 responsive to the comparison for enabling thecommunications transmitter 1306 to transmit the value of the secondvariable and to transmit a function of the value of the first variable.

[0239] Though the description of FIG. 39 is very abstract, the figurerepresents the essence of the major embodiments of the presentinvention, as the following examples will illustrate.

[0240] In a simple man-over-board monitor as illustrated in FIG. 11, thevalue 310 of the first variable is provided by a sensor 308, the value338 of the second variable is provided by a navigation receiver 304.When the sensor status 310 changes, a transmitter 314 transmits theremote unit location 338 and the sensor status 310.

[0241] In the same man-over-board monitor, when a panic button 312 isdepressed, the transmitter 314 transmits the remote unit location 338and the switch status 340.

[0242] In an environmental monitor illustrated in FIG. 18, the value ofthe first variable is a sensor status 578 for a monitored environmentalparameter, while the value of the second variable is a location 576 ofthe remote unit stored in a memory. When the sensor 558 detects apredetermined change in the monitored environmental parameter, thetransmitter 560 transmits the stored location of the remote unit and thesensor status 578. Alternatively, the remote unit 552 defines a patientmonitor, and the value of the second variable is stored information 556which identifies the patient, such as name, room and bed number, patientidentification code. The value of the first variable is the output of asensor 558 which monitors a physiological parameter, and defines asensor status 578. When a predetermined change in the monitoredphysiological parameter occurs, the transmitter 560 is activated andtransmits the patient identification information 576 as the value of thesecond variable and transmits and the sensor status 578 as the functionof the first variable.

[0243] The circuits 1308, 1310 and 1312 of FIG. 39 find theirequivalents in the man-over-board monitor, the patient monitor and inthe environmental monitor in that a change in a sensor or switch statusactivates a transmission of the value of the second variable—dynamiclocation, patient ID, and static location, respectively—and atransmission of an appropriate function of the value of the firstvariable—sensor status.

[0244] In a man-over-board monitor 752 illustrated in FIG. 21, the valueof the second variable is provided by a dynamic location determiningdevice, in this case the navigational receiver 756. Alternativeembodiments use the World-wide LORAN navigation system, a satellitenavigational system such as the GPS system, and other alternative globaland regional navigational systems for providing a value of the secondvariable which is the location of the remote unit 752.

[0245] Another example of a remote unit represented by the block diagramin FIG. 39 is a remote weather alarm 1182 illustrated in FIG. 34 inwhich the value of the second variable is a remote unit location 1187,and in which the function of the first variable is defined by a circuit1198 to be the result 1199 of a comparison of a monitored weatherparameter, within the defined zone relative to the weather alarmlocation 1187, with a defined weather threshold 1195.

[0246] Another example of the remote unit represented by FIG. 39 is aninvisible fence monitor 852 as illustrated in FIG. 24. The value of thesecond variable is a location 859 provided by a navigational receiver856, while the transmitted function of the first variable is apositional and time status 869, the result of a comparison by a circuit864 of the location 859, a time-of-day 861 and a defined curfew 860,862.

[0247] When a microphone 808 is connected to the remote unit transmitter806, as shown in FIG. 22, the remote unit of FIG. 39 includes a one-wayvoice channel.

[0248]FIG. 40 is a block diagram illustrating a remote alarm unitdesignated generally by the numeral 1320. The remote unit 1320 includesa circuit 1322 defining a first variable and providing a value 1323 forthe first variable, a communications transmitter 1324, a circuit 1326defining a condition and providing a value for the condition, a circuit1328 for comparing the value of the first variable with the value of thecondition, and a circuit 1330 responsive to the comparison for enablingthe communications transmitter 1324 to transmit a function of the value1323 of the first variable. The remote unit 1320 also includes acommunications receiver 1332 for defining a two-way communications link.

[0249] When the remote unit shown in FIG. 39 includes a communicationsreceiver, such as the receiver 1332 of FIG. 40, the communicationschannel is alternatively one of direct radio contact such as illustratedin a variety of the figures, wireless, cellular, radio telephone, radiorelay, to name a few representative communications channels as shown inFIG's 17 and 28.

[0250] An example of a monitoring system such as illustrated in FIG. 40is shown in FIG's 3, 30 and 33. In each instance, one or more sensorsand switches provide the value for the first variable and thetransmitted function of the value of the first variable is alternativelythe sensor value and the sensor/switch status. The circuits 1326, 1328and 1330 find their equivalents in an activation of the transmitter upona change of the sensor/switch status. The remote monitoring systemillustrated in FIG. 3 includes both a remote unit 82 of the class shownin FIG. 40 and a compatible base station 84.

[0251]FIG. 41 is a partial block diagram which illustrates a pluralityof sensor/switches designated by the numeral 1340. Each sensor/switch1342 provides an output signal 1343 defining a sensor/switch status. Atypical transmission format for a sensor/switch status and defining asensor/switch vector is shown in the partial pictorial diagram of FIG.42. The transmitted format is designated generally by the numeral 1350and includes a plurality of sensor/switch status bits 1352 defining astatus vector 1354. A portion 1356 ofthe transmitted format 1350 isunused and marked reserved.

[0252] Finally, FIG. 43 is a partial block diagram illustrating thetemporary connection of an input device to a remote monitor of the typeproviding a stored value for the second variable. The figure includesthe removable input device 1350 temporarily connected to the remotemonitor 1362. The remote monitor 1362 includes a circuit 1364 forstoring a value for the second variable. The input device 1350 isconnected to the remote monitor 1362 and supplies a value 1361 forstorage in the circuit 1364. Once the value 1361 has been stored, theinput device 1360 is disconnected from the remote monitor 1362, and theremote monitor uses the value stored by the circuit 1364 as the value ofthe second variable. The remote monitor 1362 corresponds to theself-locating remote alarm unit 1300 of FIG. 39, and the storage circuit1364 of FIG. 43 corresponds to the circuit 1304 of FIG. 39.

[0253] The two examples that are provided above for a self-locatingremote alarm unit which provides a stored value for the second variableare the environmental monitor of FIG. 18 and its other embodiment, thepatient monitor. Both embodiments require that a value be provided forthe second variable. A method for doing so is to connect an input device1360 to the remote monitor 1362, to use the input device to load a valuefor the second variable into the storage circuit 1364 (1304 of FIG. 39,and 556 of FIG. 18), then to disconnect the input device and to monitorthe specified environmental/physiological parameters. In one embodiment,the input device is a keypad of manually operated switches. The keypadis used to input an environmental monitor location, or, alternatively, apatient's ID information. In one embodiment of the procedure, anavigational receiver is used to provide a user with the environmentalmonitor location, which the user then enters by hand using the keypadinput device 1360 attached to the environmental monitor 1362 (552 ofFIG. 18). In another embodiment, the temporarily connected input device1360 is a navigational receiver and the location 1361 is stored in thestorage circuit 1364 (556 of FIG. 18, 1304 of FIG. 39). After thelocation has been stored in the storage circuit, the navigationalreceiver 1360 is disconnected and the environmental monitor left to doits job.

[0254] While the foregoing detailed description has described severalembodiments of the personal alarm system in accordance with thisinvention, it is to be understood that the above description isillustrative only and not limiting of the disclosed invention. Thus, theinvention is to be limited only by the claims as set forth below.

1. A man-over-board alarm system, comprising: a remote unit including anavigational receiver for receiving navigational information defining alocation of the remote unit, and a radio transmitter for transmittingthe remote unit location; a base station including a radio receiver forreceiving the remote unit location; the remote unit and the base stationdefining a separation distance between the remote unit and the basestation; the base station including measuring means for determiningwhether the separation distance exceeds a predetermined limit, and meansresponsive to the measuring means for giving an alarm and a display fordisplaying the remote unit location, whereby, a separation distanceexceeding the predetermined limit causes a man-over-board alarm and thebase station displays the location of the remote unit.
 2. Theman-over-board alarm system as set forth in claim 1, wherein the remoteunit further includes a sensor having an output signal, the sensordefining a sensor status, and the radio transmitter connected to theoutput signal for transmitting the sensor status, and the base stationincludes a display for displaying the sensor status, the navigationalreceiver further includes a low power standby mode and a normaloperating mode, and the alarm system further includes means responsiveto the sensor output signal for causing the navigational receiver toswitch from the standby mode to the normal operating mode when a hazardis detected.
 3. The man-over-board alarm system as set forth in claim 1,wherein the remote unit further includes a sensor having an outputsignal, the sensor defining a sensor status, and the radio transmitterconnected to the output signal for transmitting the sensor status, andthe base station includes a display for displaying the sensor status,the remote unit further includes a beacon activated by the sensor outputsignal when a hazard is detected.
 4. The man-over-board alarm system asset forth in claim 1, wherein the remote unit further includes a sensorhaving an output signal, the sensor defining a sensor status, and theradio transmitter connected to the output signal for transmitting thesensor status, and the base station includes a display for displayingthe sensor status, and means responsive to the sensor status for givingan alarm.
 5. The man-over-board alarm system as set forth in claim 1,wherein the remote unit further includes a sensor having an outputsignal, the sensor defining a sensor status, and the radio transmitterconnected to the output signal for transmitting the sensor status, andthe base station includes a display for displaying the sensor status,the sensor output signal is provided by a remote unit manually operatedswitch, defining a panic button, and the system includes a beaconactivated by the panic button.
 6. The man-over-board alarm system as setforth in claim 1, including a one-way voice channel linking the remoteunit with the base station.
 7. The man-over-board alarm system as setforth in claim 1, wherein the base station includes a radio transmitterand the remote unit includes a radio receiver defining two-way radiocommunication between the remote unit and the base station, including atwo-way voice channel linking the remote unit and the base station. 8.An invisible fence system for monitoring a movable subject, comprising:a remote unit including, a navigational receiver providing a remote unitlocation, means for providing time-of-day, and a radio transmitter; abase station including, receiving means defining a one-way communicationlink with the remote unit, and an alarm; the remote unit furtherincluding, a first memory for storing information defining a geographicregion, a second memory storing information defining a predeterminedpositional status and a predetermined time interval, and furtherdefining a curfew, and a circuit for comparing the remote unit location,the defined geographic zone, the predetermined positional status, thetime-of-day and the curfew, and defining a positional and time status,and the circuit connected to the transmitter for communicating thepositional and time status; the base station being responsive to thecommunicated positional and time status and defining a curfew violation,and the alarm being responsive to the curfew violation.
 9. The invisiblefence system as set forth in claim 8, wherein the remote unit transmitsthe remote unit location and the time-of-day, and the base stationfurther includes means for displaying the remote unit location and thetime-of-day.
 10. The invisible fence system as set forth in claim 8,wherein the communications link between the remote unit and the basestation receiving means includes a modem for connection to acommunications network, the network providing a portion of the completedcommunications link.
 11. An invisible fence system, comprising: a remoteunit including, a navigational receiver providing a remote unit locationand a time-of-day, a radio transmitter connected for transmitting theremote unit location and the time-of-day, a radio receiver, alarm andenforcement means responsive to the radio receiver; a base stationincluding, means for receiving the remote unit location and thetime-of-day, a first memory storing information defining a geographicalregion, a second memory storing information defining a predeterminedpositional status and a time curfew, a circuit for comparing the remoteunit location, the defined geographical region and the predeterminedpositional status, and the time-of-day and the time curfew and forproviding a positional and curfew status, a control circuit responsiveto the positional and curfew status and defining an enforcement command,and means for transmitting the enforcement command; and the remote unitalarm and enforcement means being responsive to the transmittedenforcement command.
 12. The invisible fence system as set forth inclaim 11, wherein the base station further includes means for displayingthe remote unit location and the time-of-day, and an alarm responsive toan enforcement command.
 13. A stationary environmental monitor system,comprising: a remote unit including, storage means for storinginformation defining the location of the remote unit, an environmentalsensor providing a plurality of output signals defining a sensor statusvector, an output signal and defining a sensor status, and a radiotransmitter connected for transmission of the location defininginformation and the sensor status; and a base station including, a radioreceiver for receiving the location defining information and the sensorstatus, and means responsive to a predetermined change in the sensorstatus for displaying the location of the remote unit and for providingan alarm, whereby the location of the remote unit is stored in thestorage means and a predetermined change in the sensor status causes thelocation to be displayed and an alarm to be given at the base station.14. A personal alarm system, comprising: a remote unit including anavigational receiver for receiving navigational information, ademodulator for demodulating the received navigational information,timing circuits for providing precise time-of-day information, amanually operated switch, defining a panic button and having an outputsignal defining a switch status, operation of the panic button producinga change in the switch status, and a radio transmitter for transmittingthe demodulated navigational information, the precise time-of-dayinformation, and the switch status; a base station including a radioreceiver for receiving the demodulated navigational information, theprecise time-of-day information, and the switch status; the base stationalso including computational means connected for combining the receiveddemodulated navigational information and the precise time-of-dayinformation to determine a location of the remote unit, and a displayfor displaying the location of the remote unit; and the base stationalso including means for displaying the switch status and meansresponsive to a change in the switch status for giving an alarm,whereby, the remote unit location is displayed, and the alarm isresponsive to the panic button.
 15. A personal alarm system, comprising:a remote unit including a navigational receiver for receivingnavigational information defining a location of the remote unit, amanually operated switch defining a panic button and having an outputsignal defining a switch status, operation of the panic button producinga change in the switch status, and a radio transmitter for transmittingthe remote unit location and the switch status; a base station includinga radio receiver for receiving the remote unit location and the switchstatus; the base station also including a display for displaying theremote unit location and the switch status; and the base station alsoincluding means responsive to a change in the switch status for givingan alarm, whereby, the remote unit location is displayed and a change inthe switch status produces an alarm.
 16. A personal alarm system,comprising: a remote unit including a navigational receiver forreceiving navigational information defining a location of the remoteunit, the navigational receiver having a low power standby mode and anormal operating mode, the remote unit also including a sensor fordetecting a personal hazard, the sensor having an output signal anddefining a sensor status, means responsive to the sensor output signalfor causing the navigational receiver to switch from the standby mode tothe normal operating mode when a hazard is detected, and a radiotransmitter for transmitting the remote unit location and the sensorstatus; a base station including a radio receiver for receiving theremote unit location and the sensor status; the base station alsoincluding a display for displaying the remote unit location and thesensor status; and the base station also including means responsive to achange in the sensor status for giving an alarm, whereby, the remoteunit location is displayed and a change in the sensor status produces analarm.
 17. A personal alarm system, comprising: a remote unit includingradio transmitting means, radio receiving means, at least one sensormeans for detecting a personal hazard, the remote unit transmittingmeans responsive for communicating a detected hazard; the remote unittransmitting means being able to transmit at more than one power leveland defining a higher power level, and the remote unit including meansfor enabling transmission at the higher power level when a personalhazard is detected; a base station including radio transmitting meansand radio receiving means; the remote unit and the base station defininga two-way radio communication link, and also defining a separationdistance between the remote unit and the base station; measuring meansfor determining whether the separation distance exceeds a predeterminedlimit; means responsive to the measuring means for causing the remoteunit to transmit at the higher power level when the separation distanceexceeds the limit; and alarm means for indicating when the separationdistance exceeds the limit, and for indicating when a personal hazard isdetected.
 18. A personal alarm system, comprising: a remote unitincluding radio transmitting means and radio receiving means; the remoteunit transmitting means being able to transmit at more than one powerlevel and defining a plurality of transmitting power levels; a basestation including radio transmitting means and radio receiving means;the remote unit and the base station defining a two-way radiocommunication link, and the remote unit radio receiving means defining areceived signal strength; the remote unit including control meansresponsive to the received signal strength for causing the remote unitto transmit at a power level selected by a predetermined power-levelfunction of the received signal strength; the remote unit including atleast one sensor means for detecting a personal hazard, and means forcommunicating the detected hazard to the base station; and the remoteunit including means for communicating an alarm function of the receivedsignal strength, and the base station including means responsive to thecommunication for giving an alarm.
 19. The personal alarm system as setforth in claim 18, wherein the received signal strength is furtherdefined by a voltage level on a signal line and the control meansincludes an analog-to-digital converter connected to receive the signalline and to provide digital output signals connected to address inputlines of a read-only memory, the memory containing information definingthe power-level function, the memory having digital output linesconnected for controlling the power level in response to the receivedsignal strength.
 20. The personal alarm system as set forth in claim 18,wherein the received signal strength is further defined by a voltagelevel on a signal line and the control means includes ananalog-to-digital converter connected to receive the signal line and toprovide digital output signals connected to address input lines of aread-only memory, the memory containing information defining thepower-level function, the memory having digital output lines connectedto the inputs of a digital-to-analog converter, the digital-to-analogconverter having an analog output line providing a control voltage forselecting the remote unit transmission power level.
 21. A personal alarmsystem, comprising: a remote unit including a transmitter and areceiver, the remote unit transmitter being capable of transmitting atmore than one power level and defining a plurality of power levels, abase station including a transmitter and a receiver, and defining atwo-way communications link with the remote unit, the base stationreceiver defining a received signal strength, the base stationtransmitting a command responsive to the received signal strength, theremote unit including a control circuit responsive to a received commandfor selecting the transmission power level, the remote unit including asensor for detecting a hazard, the sensor defining a sensor status, andthe remote unit transmitter connected for communicating the status, thebase station including an alarm responsive to the communicated statusfor giving an alarm when a hazard is detected.
 22. The personal alarmsystem as set forth in claim 21, wherein the received signal strength isfurther defined by a voltage level on a signal line and the controlcircuit includes an analog-to-digital converter connected to receive thesignal line and to provide digital output signals connected to addressinput lines of a read-only memory, the memory containing informationdefining a power-level function, the memory having digital output linesdefining the command for selecting the transmission power level.
 23. Aweather alarm system, comprising: a remote unit including, anavigational receiver providing a remote unit location, a weathersurveillance radar receiver providing weather parameters within apredetermined weather region, and identifying the weather region, afirst memory storing information defining a geographical zone relativeto the remote unit location, a circuit combining the remote unitlocation and the geographical zone to define a local weather zone, asecond memory storing information defining at least one weatherparameter threshold, means for determining that the local weather zoneis within the identified weather region, and that a received weatherparameter exceeds the at least one weather parameter threshold, atransmitter connected to communicate the result of the determination;and a base station including means responsive to the communication forgiving an alarm and for displaying the result of the determination. 24.The weather alarm system as set forth in claim 23, wherein thenavigational receiver also provides a time-of-day, and the transmitteralso communicates the time-of-day for display by the base station. 25.The weather alarm system as set forth in claim 23, wherein thetransmitter also communicates weather parameters for display by the basestation.
 26. The weather alarm system as set forth in claim 23, whereinthe base station means responsive to the communication includes a radioreceiver.
 27. The weather alarm system as set forth in claim 23, whereinthe base station means responsive to the communication includes a modem.28. The weather alarm system as set forth in claim 23, wherein thenavigational receiver includes a low-power standby mode and a normaloperating mode and is responsive to the determination for switching fromthe standby mode to the normal operating mode.
 29. A personal alarmsystem remote unit, comprising: a radio transmitter and radio receiverfor providing a two-way radio communication link; a navigationalreceiver for providing a location of the remote unit; a manuallyoperated switch defining a pair of electrical contacts for providing anoutput signal; the radio transmitter connected for transmitting theremote unit location and the switch output signal; and a microphone andspeaker connected with the radio transmitter and receiver for providinga two-way voice channel via the two-way radio communication link. 30.The personal alarm system remote unit as set forth in claim 29, whereinthe radio transmitter and receiver comprise a wireless telephone for usewith a wireless telephone network.
 31. The personal alarm system remoteunit as set forth in claim 30, further including means connected to themanually operated switch for initiating a wireless telephone call to the911 dedicated public safety help telephone number.
 32. The personalalarm system remote unit as set forth in claim 30, wherein the wirelesstelephone is a cellular telephone for operation with a cellulartelephone network.
 33. The personal alarm system remote unit as setforth in claim 30, wherein the wireless telephone is a personalcommunications services telephone for operation with a personalcommunications services telephone network.
 34. The personal alarm systemremote unit as set forth in claim 30, wherein the wireless telephone isa radio telephone for operation with a radio telephone network.
 35. Thepersonal alarm system remote unit as set forth in claim 30, furtherincluding a plurality of manually operated switches connected forselectively initiating telephone calls to any one of a plurality ofpredetermined telephone numbers.
 36. The personal alarm system remoteunit as set forth in claim 35, wherein one of the predeterminedtelephone numbers is the 911 dedicated public safety help telephonenumber.
 37. The personal alarm system remote unit as set forth in claim35, further including means for manually programming at least some ofthe predetermined telephone numbers.
 38. A remote unit, comprising: acommunications transmitter; a circuit for providing a first variablehaving a value; a circuit for determining whether a predetermined changein the value of the first variable has occurred; a circuit for providinga second variable having a value; and the communications transmitterconnected for transmitting the value of the second variable and thevalue of a function of the first variable when the predetermined changein the value of the first variable has occurred.
 39. The remote unit asset forth in claim 38, wherein the circuit for providing the firstvariable is a sensor having an output signal and the value of the firstvariable is an electrical parameter of the output signal and defines asensor status, and the transmitted function of the first variable is thesensor status.
 40. The remote unit as set forth in claim 39, wherein thecircuit for providing the first variable includes a plurality ofsensors, each having a sensor output signal having a value defined by anelectrical parameter of the sensor output signal, and wherein theplurality of sensor output signals defines a sensor status vector, andthe communications transmitter is connected for transmitting the sensorstatus vector, and wherein the circuit for determining whether apredetermined change has occurred determines whether a predeterminedchange has occurred within the defined status vector.
 41. The remoteunit as set forth in claim 38, wherein the circuit for providing thefirst variable is a pair of electrical contacts defining a manuallyoperated switch, and wherein the value of the first variable is one of aclosed circuit and an open circuit defining a switch status, and thetransmitted function of the first variable is the switch status.
 42. Theremote unit as set forth in claim 41, wherein the manually operatedswitch defines a panic button.
 43. The remote unit as set forth in claim41, wherein the circuit for providing the first variable is a pluralityof switches, and wherein the value of the first variable defines avector of values, each value being one of a contact closure and an opencircuit, defining a switch status vector, and the transmitted functionof the first variable is the switch status vector.
 44. The remote unitas set forth in claim 43, wherein the plurality of switches defines amanually operated numeric input device.
 45. The remote unit as set forthin claim 43, wherein the plurality of switches defines a manuallyoperated alphanumeric input device.
 46. The remote unit as set forth inclaim 38, wherein the circuit for providing the second variable is ameans for storing a number, and the value of the second variable is thestored number.
 47. The remote unit as set forth in claim 46, furtherincluding means for providing a patient identification code for storageas the value of the second variable, and wherein the circuit forproviding the first variable includes at least one sensor for monitoringa physiological environmental parameter and defining a sensor status,the transmitted function of the first variable being the sensor status,and the remote unit defining a patient monitor.
 48. The remote unit asset forth in claim 46, further including means for connecting an inputdevice for providing the location of the remote unit for storage as thevalue of the second variable, and wherein the circuit for providing thefirst variable includes a sensor for monitoring an environmentalparameter and defining a sensor status, the transmitted function of thefirst variable being the sensor status, and the remote unit defining anenvironmental monitor.
 49. The environmental monitor as set forth inclaim 48 in combination with a plurality of manually operated switchesfor providing the location of the remote unit.
 50. The environmentalmonitor as set forth in claim 48 in combination with a dynamic locationdetermining device for providing the location of the remote unit. 51.The environmental monitor as set forth in claim 50, wherein the dynamiclocation determining device is a navigational receiver.
 52. Theenvironmental monitor as set forth in claim 51, wherein the navigationalreceiver operates with a satellite navigational system.
 53. A method forremotely monitoring an environmental parameter, comprising the steps of:providing an environmental monitor as set forth in claim 48; providingan input device for supplying a number representing a location;connecting the input device to the environmental monitor via theconnecting means; determining the location of the environmental monitor;using the input device to provide a number corresponding to the locationof the environmental monitor; storing the number in the number storingmeans; disconnecting the input device from the connecting means;monitoring an environmental parameter; activating the communicationstransmitter when a predetermined change in the value of the monitoredparameter occurs; transmitting the sensor status and the stored locationof the environmental monitor.
 54. The method as set forth in claim 53,wherein the input device is a plurality of manually operated switchesand wherein the location of the environmental monitor is determinedusing a GPS receiver, and the number representing the location forstorage in the number storing means is entered using the manuallyoperated switches.
 55. The method as set forth in claim 53, wherein theinput device is a GPS receiver having means for connecting to theenvironmental monitor, the receiver being operated to determine theenvironmental monitor location and to provide a number representing thelocation for storage in the number storing means.
 56. The remote unit asset forth in claim 38, wherein the circuit for providing the secondvariable is a dynamic location determining means, and the value of thesecond variable is the location of the remote unit.
 57. The remote unitas set forth in claim 56, wherein the dynamic location determining meansis a navigational receiver.
 58. The remote unit as set forth in claim57, wherein the navigational receiver is a LORAN receiver.
 59. Theremote unit as set forth in claim 57, wherein the navigational receiveris a satellite navigational system receiver.
 60. The remote unit as setforth in claim 59, wherein the satellite navigational receiver is a GPSreceiver.
 61. The remote unit as set forth in claim 57, wherein thecircuit providing the first variable is a water immersion sensor andwherein immersion of the remote unit in water activates thecommunications transmitter for transmitting the remote unit location,the remote unit defining a man-over-board monitor.
 62. Theman-over-board monitor as defined in claim 61, further including abeacon activated when the monitor is immersed in water.
 63. Theman-over-board monitor as set forth in claim 62, wherein the beacon is avisual beacon.
 64. The man-over-board monitor as set forth in claim 62,wherein the beacon is an audible beacon.
 65. The man-over-board monitoras set forth in claim 61, adapted for operation from a battery andenclosed in a waterproof floatation device.
 66. The man-over-boardmonitor as set forth in claim 65, wherein the waterproof floatationdevice is a life vest.
 67. The remote unit as set forth in claim 57,wherein the circuit for providing the first variable includes: a weathersurveillance radar receiver providing weather parameters within apredetermined weather region, and identifying the weather region, afirst memory storing information defining a geographical zone relativeto the remote unit location, a circuit combining the remote unitlocation and the geographical zone to define a local weather zone, asecond memory storing information defining at least one weatherparameter threshold, means for determining that the local weather zoneis within the identified weather region, and that a received weatherparameter exceeds the at least one weather parameter threshold, and thecommunications transmitter connected to communicate the result of thedetermination and defining a remote weather alarm whereby a geographicalzone is specified and weather parameters within the zone are monitoredand compared with parameter thresholds and the result of the comparisonis transmitted, permitting remote monitoring of weather conditionswithin a predefined region.
 68. The remote weather alarm as defined inclaim 67, further including the navigational receiver providingtime-of-day and the communications transmitter connected to communicatethe time-of-day.
 69. The remote weather alarm as defined in claim 67,further including the communications transmitter connected forcommunicating received weather parameters.
 70. The remote weather alarmas defined in claim 67, further including the first and second memoriescombined into a single memory.
 71. The remote unit as set forth in claim57, wherein the circuit for providing the first variable includes: meansfor providing time-of-day, a first memory for storing informationdefining a geographic region, a second memory storing informationdefining a predetermined positional status and a predetermined timeinterval, and further defining a curfew, and a circuit for comparing theremote unit location, the defined geographic zone, the predeterminedpositional status, the time-of-day and the curfew, and defining apositional and time status, the positional and time status defining thevalue of the first variable, the remote unit defining an invisible fencemonitor, and the communications transmitter connected for communicatingthe positional and time status.
 72. The invisible fence monitor asdefined in claim 71, wherein the positional and time status define acurfew violation and the monitor includes alarm and enforcement meansresponsive to the curfew violation.
 73. The invisible fence monitor asdefined in claim 71, wherein the first and second memories are combinedto form a single memory, so that the information defining a geographicregion and the information defining a curfew are stored in the singlememory.
 74. The invisible fence monitor as defined in claim 71, whereinthe communications transmitter is connected to transmit the monitorlocation and the time-of-day.
 75. The remote unit as set forth in claim38, further including a microphone connected to the communicationstransmitter for providing a one-way voice channel.
 76. The remote unitas set forth in claim 38, further including a communications receiver.77. The remote unit as set forth in claim 76, wherein the communicationstransmitter and the communications receiver are adapted for operationwith a radio relay system.
 78. The remote unit as set forth in claim 76,wherein the communications transmitter and the communications receiverare adapted for operation with a radiotelephone system.
 79. The remoteunit as set forth in claim 76, wherein the communications transmitterand the communications receiver are adapted for operation with acellular telephone system.
 80. The remote unit as set forth in claim 76,wherein the communications transmitter and the communications receiverare adapted for operation with a personal communicator system.
 81. Theremote unit as set forth in claim 76, wherein the communicationstransmitter and the communications receiver are adapted for operationwith a wireless communications system.
 82. The remote unit as set forthin claim 76, further including a microphone connected to thecommunications transmitter and a speaker connected to the communicationsreceiver for providing a two-way voice link.
 83. A remote unit,comprising: a communications transmitter; a circuit for providing afirst variable having a value; a circuit for determining whether apredetermined change in the value of the first variable has occurred;the communications transmitter connected for transmitting the value ofthe first variable when the predetermined change in the value of thefirst variable has occurred; and a communications receiver.
 84. A remotemonitoring system, comprising: a remote unit including, a communicationstransmitter, a circuit for providing a first variable having a value, acircuit for determining whether a predetermined change in the value ofthe first variable has occurred, the communications transmitterconnected for transmitting the value of the first variable when thepredetermined change in the value of the first variable has occurred,and a communications receiver; and a base station including, acommunications transmitter, a communications receiver defining a two-waycommunications link with the remote unit, and the base station includingalarm and display means responsive to a received value of the firstvariable.